I have a slightly different point of view from most of the comments here so far.
1. Your #1 priority really has to be your family. I'm not assuming your family isn't important to you -- clearly it is -- but, it has to be more important than building a product or starting your own company. You're spending at minimum 65 hrs/week doing "not family", and that's a bit too much. You have 1.5 young kids, and what you do now, as a parent, will shape their future for the next several decades. It will change how they relate to other people, how they raise their own kids, and so on. If you want to have an impact on the world, focus on raising your kids.
2. So your job is your job. I mean, separate your self-worth from your employer. Show up, do what they ask, collect a paycheck, go home. One of the best things I ever did was step out of the computer industry for a few years and pick up a bunch of different jobs, including retail. I will still happily put in a lot of extra effort for any employer that wants it and is willing to reward me for it, but I can also show up every day, do the job, and go home, and have lots of other things to care about other than what's going on at work.
3. That said, if you can't learn how to do that, just show up and do the work and go home and forget about it, then you have to keep looking for a new job. That really should be your spare time gig, IMO, before other projects. It becomes your responsibility as a parent to try to find a job that values you and wants to pay you more so that you can provide more financial stability for your family -- and the best way to do that is with a better job, not a startup. HN is about the worst place to get this kind of life advice, because it's heavily skewed towards the attraction of risk-taking and the success stories when those risks pay off, but the reality is that the odds are not in your favor. There are a lot of bright and talented and ambitious people here on HN -- thousands, at least -- and of those, maybe only a handful have found something resembling wealth and stability, and of those, I'd bet most of them went through some pretty bad times. Do you really want to try to juggle all of that and a family at the same time?
I'm not saying you shouldn't work on your project at all, but that your priorities should probably be family, better job, and then project, in that order.
And, the consistent advice on HN is not to worry too much about being beaten to market. If someone else gets there first, it gives you an opportunity to see if there is a market at all for your product without having to suffer through the market research yourself (which these days typically consists of, "gosh, I really hope someone buys my product/service"), and you get to see what kind of mistakes they make, and learn from them. If it's a good market, there will be room for at least two of you.
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There's a thing I do whenever I'm faced with really difficult life decisions. I sit back, let things get really quiet, close my eyes, and I try to see my futures stretching out in front of me like roads going in different directions. Each road represents a decision, and stretching out past my decisions aren't my fantasies but the most realistic outcomes I can guesstimate for each.
So, I would close my eyes, and I would see a road going off to the left, and that road goes like this: work full time for job I dislike, work hard on startup/side project, try to raise family on the weekends ... I am tired, and I am stressed out, because it's impossible to do all of that without getting tired and stressed out. Stress puts a strain on my relationship with my family. Project is completed and launched, and now I try to juggle a full time job, running a business, and raising a family. My health suffers. My oldest kid is 5 years old, and the business is still going. It hasn't failed, but it hasn't been a wild success either. I still pick up consulting jobs here and there to supplement my income. My kid is 10, and the business is stable now, but our relationship is a bit distant. I am responsible for two kids and a wife and a business and I lay awake at night occasionally thinking about that. There is a small disaster or two -- car accident, economic downturn, a health issue -- because few people get to go 10 years without a serious challenge in life. I am able to handle it but it's difficult. My eldest is 15 now, a rebellious teenager, and s/he knows exactly what to say to punch me in the heart: what do you care, you're always busy working anyway. The business is successful, we spend some of the hard-earned money on trips and a few luxuries.
Off to the right is a road that goes like this: work full time for job I dislike, swallow my pride and hopes and dreams and put down my project for a while -- just a while. I practice tolerating the job while actively looking for a new job and trying to squeeze the occasional raise out of the current one. A year later, I have a new job. I don't like it much better, but it pays more. I don't stop looking for new opportunities. I come home and have dinner with the family and spend time with the wife and kids. I'm not happy or fulfilled at work, but I can come home and leave the stress at work. I still poke at my project now and again, I take shortcuts, but I make progress on it as a hobby. Another year later, another new job, another raise. I take a small risk and hire a cheap freelancer to finish out a few things on my project. Somebody else beat me to market and they're doing well but their customer support forums are full of complaints. I launch my project, still incomplete, but I don't have to be stressed out about that -- my income doesn't depend on the success or failure of this project. 5 years later, and I own my own business, but over the years I've developed a strong habit of spending time with my family. I have a little bit of savings in the bank and my health isn't too bad. The business isn't wildly successful, and we've had to give up a few luxuries, but it pays the rent and does OK.
That's how I'd figure it anyway. Maybe there are other options too. Really try to envision each scenario. Try to feel like you're living in them. Try to make them realistic. Don't fall into the trap of assuming that a good idea and a lot of hard work is enough to guarantee success.
And think of your family as your first startup.