Raising 5 boys, with 3 still at home with a non-biking wife. I have gladly taken on the role of family bike mechanic, because I like to work on bikes. I have trained the older boys on basic maintenance tasks. 2 bikes have been handed down at least 3 times, with a few others handed down once or twice.
Craigslist is my friend.
Your family is sort of like mine, though I only had two girls, but now I have grandkids so slowly but surely they too will be needing my services for their bikes, and we have a teenage friend who's dad died and he stays with us on most weekends and I've taught him some stuff on how to fix his bike and he's helped me dabble with my cars so he'll know some things when he gets one. And my wife isn't a big cyclist either, she thinks she's gone far when she pedals for 7 miles. She thought I was nuts for years riding as much as I do, but she's use to me doing that after 30 plus years.
This is one of my favorite parts of being a dad, taking care of all the bikes in the garage. I get the kids to help pump up the tires, oil the chains, and do the general pre ride brake checks. The rest of the stuff I have to take care of on my own, the kids are too young to stay engaged and really care about fixing derailleurs.
I've started to take on work from my neighbors, too. THere are a couple of kids around here who's dads can't fix anything, and I'm trying to teach those kids how so we can get rid of the "un-handy" gene in one generation, rather than let it get passed on.
I fix all the bikes for me and my wife and my son and his family. My grandson has been riding a 2 wheeler since he was 3. He is now 6 in the spring I am going to buy him a complete bicycle tool box and teach him how to repair his own bike.