The house upstairs leaked water, but refused to sign an agreement with my family, asking my family to sign it with the decoration company.

There is no need to sign any agreement with the upstairs owner. In this case, the upstairs owner should take full responsibility. Of course, if there is a problem with the construction of the decoration company, you can sue the other decoration company together when complaining about rights protection.

The upstairs owner wants to shirk his responsibility by asking for a decoration company, and the decoration company can't sign any agreement with you. Because their service object is only your upstairs owner, not you, and they are only responsible for the upstairs owner, it is unrealistic to ask them to sign any agreement.

I hope I can help you. Welcome to consult.