If we sell a house in a trust(4 of us)how much will be considered capital gains? All of it? A percentage?

This question is REALLY too complex to answer on this forum.

Any advice given would be done without knowing the terms and conditions of the trust, and could be completely wrong in the absence of that knowledge.

Recommend you contact a local tax professional with experince in trust work, make an appointment and have him analyze the trust documents in order to give good advice.

Can you sell the house with owners that have shares in it but don't want to sell the houses

That is actually a LEGAL question best posted in the LAW Forum.

can you sell the house with owners that have shares in it but dont want to sell the houses

It depends on how the property is titled. If "Joint tenants" or "Joint tenants with rights of survivorship" then no - you all have equal stake in ownership and all must approve the sale. But if titled as "Tenants in common" then you each own a portion independent of the others, and you can sell your fractional share as you wish. The buyer then becomes a fractional owner. Also if there is a mortgage on this property then all owners must be involved as a new mortgage will be required.

My suggestion is if you want to sell your portion your best bet is to negotiate with the other co-owners to buy you out.