Unless you feel like you are also going to become best friends I suggest you be aware that it’s highly likely your opinion will matter the least, mistakes by team members will be difficult to highlight, you will be unlikely to get promoted or be acknowledged as being as valuable as the friends. It does depend how many people there are currently; if it’s more than four I’d stay away if it’s less than four you can say to them and think like you are employee number 1.

I’d ask them about the things I’ve suggested might be problematic and if their reaction is anything but thoughtful comments on how to fix such things for you run away.

Finally for me it’d be about the idea, if I was passionate about it I’d find a way to make it work probably but then I care more about the product that’s made than even the people.