You can stop the sale with a court order, which you can get by filing a legal action (lawsuit): it takes a majority of the ownership or control to sell assets, but if there are four of you, each with 25% and two of you (owning between you 50%) do want and did not consent to the sale, the other two cannot sell. Procedurally, getting a court order on short notice can be difficult; retain an attorney to help. The important thing is, with four equal owners, it takes three of them to make a sale of assets happen.