It's mostly a list of things that happened before concluding that the anarchists were completely unprepared for partial success which caused them to fracture and ally them selves with various lesser-of-two-evil factions which further fractured them leading to their eventual irrelevance.
Not just in Spain, in USSR and elsewhere too.
In fact the ideological enmity between communists and anarchists starts even back at the time of Bakhunin and Marx (and they were many critiques from one to another).
They were exploited and betrayed, but the same could be said for the majority that stayed home and later were sent off to be slaughtered by the power that the USA worked with "against communism". And at the least the CPUSA volunteers had some agency.
Eby's book is good though.
Of course we could say that at the time it was too hard to see, but Purges had already been going on for long, with millions dead in murders and famines, and people knew. Many just chose not to believe.
Hitler was as involved in the Spanish civil war as Stalin. During the following great war, the allies decided that Stalin was the lessor of the two evils, and I think that history has largely judged that to not have been the wrong decision.
There was also the fact that they didn't had many legs to stand on.
What Stalin did to its own people, the western powers did the same and worse in their colonial territories. Mass executions, dictatorships, torture, forced labour, police brutality, concentration camps, state-caused famines, and the like.
Just one example: "On the pretext of a slight to their consul, the French invaded Algeria in 1830. Directed by Marshall Bugeaud, who became the first Governor-General of Algeria, the conquest was violent, marked by a "scorched earth" policy designed to reduce the power of the native rulers Dey; this included massacres, mass rapes, and other atrocities. Between 500,000 and 1,000,000, from approximately 3 million Algerians, were killed within the first three decades of the conquest."
It didn't continue any better than that. In fact, until the very 60s, decades after WWII ended, the police beat to death 100 demonstrators, not in some remote backwater, but in Paris itself:
https://en.wikipedia.org/wiki/Paris_massacre_of_1961
And that's just one example from France. There are many other examples from France, Britain, Belgium, and so on.
Besides, they could not care less for the Jews. What they wanted, and fought Germany for, was not to let it rule the world (trade lines, developing nations, crucial territories and so on) -- the same thing WWI, WWII, and the Cold War happened for.
Good thing that they were betrayed and a very good thing would have been all of them being killed in the war. He who lives by the sword, dies by the sword.
Those guys that wanted revolution should have started it in their own house first.
The Russians managed to acquire millions of dollars of gold reserves from the Republic in exchange for a disappointing array of weaponry, distributed only to their cronies, and accompanied by incompetent military advisors who were more interested in looking good back home than in winning the war. The anarchist unions seem to get more respect, but there's a strong argument that they were militarily ineffective, that their resistance to the Russia-aligned PSUC was destabilising at a critical period, and that the middle of a war against ascendant fascism was not the greatest time in the world to start redistributing land and making enormous social reforms. That's not even getting into Catalan/Basque independence, all the little minor parties, the different police factions, the wave of assassinations that led up the war (though fewer in number and in response to similar assassinations), the immense difficulty of forming a stable government, etc.
Reading into the war gave me a greater awareness of exactly how badly the "good guys" can behave, while in no way mitigating the horrors the Nationalist faction committed.
My grandfather's father and a substantial part of my grandmothers family (her father, brother, ...) were killed by anarchist because they were Catholics and because they were bourgeois (on one side they were a declining industrial family and on the other side they were doctors and pharmacists). They came one night, they put them into trucks and they never came back.
That was their crime, to go to church every Sunday, to be richer than the average, and have studied at the university. So the part of the family that survived had to support Franco, it was a question of survival.
Franco's side did the same with communists and anarchists, so many people had to join radical left-wing militias, more radical than themselves, just to survive.
There is nothing to romanticize about the Spanish Civil war. There were no good guys, it was all chaos, injustice and death all over the place, and today we still pay the consequences of so much stupidity.
I don't want to get too personal, as I lack the historic details in your case, but as far as I know the republic and the anarchists were not at all the same. And anarchists that killed rich people for being rich and catholic alone ... might have existed, but not as the norm and rather a very extreme subgroup. There is no common anarchistic ideology that justify this. So maybe there was a bit more to it, like beeing member of the falangists as well? (Even then it would be against common anarchistic ideology in general, but more likely)
So I doubt the choice of your family was binary. Understandable, given that they were catholic and franco was on the catholic side ... Maybe. But not the only choice.
But in general I very much agree. Not much to romanticize about a civil war. Heroic deaths here and there, yes. But mostly blood and hate.
It is a small town, quite remote. Soldiers (no officers are present, as the officers supported Franco's military coup and were sentenced to death for that just at the beginning of the war) and militia men are in control. They burn the churches, kill the priests and kill your father and your older brother, together with other men in town that are guilty of being "bourgeois" and Catholic. None of these assassinated men had weapons. They were right wing civilians, which doesn't make them fascists, because they weren't. After a few months of suffering and going to sleep every night wondering if tonight is the night they will com for you, the Republic finally sends some officers. This improves the situation and puts some order, but, still you feel pressured every time you leave home. At then end of the war, Franco's troops enter town. You feel relieved, as you know you are now safe. However, at the same time, you suffer because it is now the families of the other side, people that you know, that will suffer as you suffered until now. Franco's secret police comes to visit you to ask you to testify against those who killed your family members. You say no, because you are Catholic and, thus, against revenge. Franco's police, surprised, investigates you, but at the end absolves you.
That's how happened, more or less, in one side of my family. Every day during the war they hoped Franco would win, but they were no fascists, they didn't really believe in the guy, they valued Catholicism and just wanted to survive.
I just want to point out that once inside a war, there are no good guys and you end up choosing the side that is not going to kill you. This doesn't mean you support what this side is doing to the other side.
I think in Syria something similar is happening. Many people that know that Assad is a butcher, are supporting him because they fear more the alternative than the butcher. This happens to many Syrian Christians who fear that salafists will kill or expel them if they win the war. So, even though they despise Assad, they want him to win the war.
Addition: So, sometimes you don't choose sides, the sides choose you, mainly, negatively, they consider you an enemy and thus you end hoping the others win, even if you despise them.
Currently, in Spain, a lot of left wing people have an idealistic view of the war that I find dangerous.
Also, there is still too many people downplaying Franco's brutality.
I fear that this condemns us to make the same errors again.
Well, each to his own likings I guess.
But you know "missguided" socialists killed people for being born rich and fascists killed people for being born jewish. Sounds pretty similar to me.