my neighbor who is my brother put in a pool which some of it extends on my property- they are getting a divorce and I am concerned about this- the pool was there before I boutght the property but the land the pool is on was not deeded to them-can they sell
without my deeding the property to them?

It is an encroachment which they would have to disclosed in the Seller’s Disclosure. You can sell it, but who knows what a Buyer will do.I suggest talking to a Real Estate Attorney.