Bronze,
I'm a CPA so I deal with items like this regularly. While everything your parents are doing is likely very legal and above board, nothing they are doing sounds fair to you. A few points/clarifications from yours and other comments:
1) Someone mentioned you are entitled to 40% of the profits. While this is correct, and I'm sure 40% of the profits are allocated to you on your K-1 each year, this does not "entitle" you to 40% of the available cash every year. Most partnership agreements will provide for a payment of cash to cover your tax liability, but some simply don't. It doesn't sound like your partnership is required to make "tax distributions" since it isn't.
2) If your parents have control of the partnership, which they can have in various ways, they have full authority to make any decisions related to the operations, including what to do with all the cash. If they are General Partners and you are a limited partner, it's likely they have full control, even if they only own 1% of the partnership.
3) Someone else mentioned a partnership requires a pro-rata distribution (i.e.-you own 40% so you get 40% of all cash distributions). I believe they are confusing partnerships with S-Corps. Partners in a partnership can take a "draw" from their equity, however this is likely subject to approval of the controlling partner. This does not have to be pro-rata. In direct contrast, S-Corps are required to pay pro-rata distributions at all times to avoid major IRS consequences.
4) MOST IMPORTANT ITEM - This one is in your favor substantially; therefore it's likely detrimental to your parents - By paying taxes on your profits, but not actually receiving any of the cash, you have built up a very large partnership basis. This means when your interest is sold, the building is sold, or you obtain control of your future cash "draws", you will not be paying much tax. If the building is sold you will likely pay capital gains, but your "Partnership Basis/Cost Basis" for the sale will be very large due to all the profits you've paid taxes on. If you sell your partnership interest the same thing is true, lower taxes due to your current situation. When/if you ever gain control of the partnership, or when you are able to begin drawing cash out, you will not pay taxes on the cash you take out. You will continue to pay taxes on the profits, but not the cash. However, all cash you take out will reduce your partnership basis (cost basis in the partner interest).
Summary - It's likely legal, but not fair based on all the facts you provided. I'm glad they decided not to fund your brother's lifestyle with your company. If you stick with it you will have some major tax benefits in the long run once you start to see some cash from this operation.
And no, you are not an ungrateful future heir. Good Luck.