Get some moving blankets on the walls and/or DIY some sound deadening panels.
quick youtube search.
https://www.youtube.com/watch?v=pABvTWSxOes
this one uses old bathroom Towels in a panel. Make 3-4 of them and hinge them together and you have a freestanding movable partition/sound deading panel. I did something like this to deaden sound when recording in my house.
Love this guys channel. Great builds.