Go buy 2 big cheap tupperware containers.

Toss all that stuff in it.

Place it in the basement or garage.

When he comes over. Tell him you packed it up already for him and tell him where the containers are.

Let him move them out.

You have already helped.

As for the mattress. Remove it. Say nothing. Do what you need to do to live in your house.

ITS YOUR HOUSE.

Remember removing stuff can be very therapeutic.