I think that a March or April use year would be perfect for you. You will receive those points on the 1st of either March or April, and then you will have until Oct 31 or Nov 30 (respectively) to use those points before you'll need to bank them. If you don't plan on vacationing from Nov - Feb or Dec - March then you will be fine.
I come from a close family, as does my wife, so doing what you're doing does not sound strange. I will, however, add that you should definitely find the same use year for the three separate contracts. Also, considering you are all only interested in BCV, having that be your home resort is the best option for you because that resort does not usually see the 7 month booking window. (if you don't know what I'm talking about...you can book at your home resort 11 months before your trip. If you stay at a resort that is not your home resort, you will have a 7 month booking window)
It sounds like you're planning on purchasing via resale. Good choice if that's the plan. I will let you in on a little not so secret haha. Once you are a member, even if it's via resale, you can purchase a minimum of 25 points through Disney. Doing that will give you access to the discounts. In case you didn't know, Disney cut the discounts from people that buy via resale last year. Meaning, no discounted park passes or discounts on merchandise, etc. So, buy your three 100 point contracts and if you want those
DVC discounts and benefits, buy 25 points through Disney. If you don't care about any of that, don't buy 25 from Disney. lol It's that simple.
Again, when buying your contracts, be patient and wait for the same use year. Buying different use years will make your life more complicated and it could possibly limit their ability to vacation together in the future.
Don't worry about missing a vacation one summer, bank those points and make your following vacation an even bigger one!
Keep doing your research and look up the
points charts online. Typically you can stay in a deluxe studio, a one bedroom villa, a two bedroom villa or a three bedroom villa. Summer is a peak season which result in higher points per night. Once you figure out the kind of room you want and then amount of nights you want to stay, you'll have a better insight as to how many points you'll actually want.