Partnership Agreement?

You do not need a written partnership agreement to have a partnership. However, without a written agreement it becomes hard to prove what your agreement was or even if there was a partnership. Why would you need to prove it to anyone? No matter how good your friends are, when thousands of dollars are involved it is amazing how quickly your understanding of your arrangement changes. Not only does having a written agreement tend to prevent drifting understandings, it helps if you need some authority (courts, mediation, arbitration) to resolve a disagreement on what you meant.

By not being on the title, you are in a very weak position. You probably sense this as you get closer to a sale (which is why you are asking). If you are not on the title, the buyer can give all the sale proceeds to your partners and your partners can give the buyer the property. It will be up to you to try to get your share from your partners after they have been paid. At that point you will have very little leverage, and with no written agreement as well you will have to rely on the good faith of your partners to hand over potentially thousands of dollars. This is almost guaranteed to be a disaster in the making.

I highly recommend you consult an attorney about options for minimizing your risk. While it is attractive to get some thoughts from this board, it is no substitute for attorney representation. These answers are general thoughts about legal principals. Solutions to your particular problem can only come from an attorney you retain to represent you.