Get a lawyer and do it quick.
Did you sign a contract with the potential buyers??? Or a contract with the real estate agent to sell it????
The survey should have been done BEFORE any contract was signed... MOOT POINT now...
I am not sure what all you can do since you agreed and now you are changing the terms. If they only agreed verbally, to let you have the "new property lines" along where the fences currently are, and it has not been resurveyed and recorded, you may have no options.
You may have to break the contract and eat the costs, penalties, etc... if you do not want to sell the land where the fences are... or else move the fences..
And 90 ft easement is absurd ...
You can say you do not want to sell it, and all according to the way the real estate contract is worded, you will pay some costs and penalties... Unless it is a bank foreclosure, there are ways to "not sell it"... but it will cost you.
These people are going to be more than just the problem I suggested back several pages ago.... they are going to be a nightmare... Find a way to cancel this and STOP the sale.
Your real estate agent did not do you any favors to start with, it should have been surveyed before putting it on the market since this is a "subdivide"......then the people wondering if cattle smell, then you changing your mind because the fences were so far off where the survey was showing... If the original agreement showed a 90 ft easement... then it is not unfair for them to want a smaller one, but more than you want to provide, because you do not want to move fences... That is not their problem... it is yours.
Understand I am not siding with them... but you have legal obligations once you sign a contract.
If the contract is with the real Estate person, and NOTHING is signed with the prospective buyers... then you have alot more rights and abilities to say no.... if you already Accepted a signed agreement/contract with the prospective buyers, then you have a different set of problems...
GET A LAWYER... you are in over your head and the RE agent is NOT doing you any favors... Like you said; it is the $$$$$$ signs that she is seeing.
You need to know where you stand and what you can do... NOW.