I would suggest, both as an investor and as someone who has some experience with a family-run trust (not my own), that this is probably not something you should get involved with, unless the money is money you're not worried about - money that otherwise would turn into trips to the movies or something like that. If you're willing to treat it as such, then I'd say go for it.
First off, this is not a short or medium term investment. This sort of thing will not be profitable right away, and it will take quite a few years to become profitable to the point that you could take money out of it - if ever. Your money will be effectively, if not actually, locked up for years, and be nearly entirely illiquid.
Second, it's not necessarily a good investment even considering that. Real estate is something people tend to feel like it should be an amazing investment that just makes you money, and is better than risky things like the stock market; except it's really not. It's quite risky, vulnerable to things like the 2008 crash, but also to things like a local market being a bit down, or having several months with no renter.
The amount your fund will have in it (at most $100x15/month) won't be enough to buy even one property for years ($1500/month means you're looking at what, 100-150 months before you have enough?), and as such won't have enough to buy multiple properties for even longer, which is where you reach some stability. Having a washing machine break down or a roof leak is a big deal when you only have one property to manage; having five or six properties spreads out the risk significantly.
You won't get tax breaks from this, of course, and that's where the real issue is for you. You would be far better off putting your money in a Roth IRA (or a regular IRA, but based on your career choice and current income, I'd strongly consider a Roth). You'll get tax free growth, less risky than this fund AND probably faster growing - but regardless of both of those, tax free. That 15-25% that Uncle Sam is giving you back is a huge, huge deal, greater than any return a fund is going to give you (and if they promise that high, run far and fast).
Finally, as someone who's watched a family trust work at managing itself - it's a huge, huge headache, and not something I'd recommend at least (unless it comes with money, in which case it's of course a different story). You won't agree on investments, inevitably, and you'll end up spending huge amounts of time trying to convince each other to go with your idea - and it will likely end up being fairly stagnant and conservative, because that's what everyone will be able to at least not object to. It might be something you all enjoy doing, in which case good luck - but definitely not my cup of tea.