But frankly: 3 devs * 5 months and you have nothing? This is a no go for every investor, i am sure.
But, your point stands.
Having a few junior devs around the experienced devs is okay, but only inexperienced devs (in the technology at hand) is a really bad situation.
Or choose a stack the developers know.
The two devs also come from Ruby and stated it'd be more work than it's worth to move to that stack.