WIBTAH if I refused to help sell my partner’s dad’s belongings?

My partner and I are moving long distance and I’m paying for the move by myself, so we’re trying to get rid of almost everything we don’t need because moving is ridiculously expensive.

His dad moved to the UK years ago (a permanent move) and left behind about half a house worth of belongings. Now that we’re unexpectedly selling the house, he wants us to either buy a lot of it from him, move it, or sell it for him. Importantly, he doesn’t want to pay for the shipping of things to him directly.

The problem is “selling it” means taking pictures of literally hundreds of individual items… making listings, answering messages, being the middle man negotiating prices, coordinating pickups, etc. My partner has already spent well over 24 hours doing this and has barely made a dent. Meanwhile we get nothing from this and we’re not even doing that with our own unwanted stuff because it isn’t worth the time. We just have a few weeks left now to moving day.

To be fair, 1) he only found out about the sale a few months ago. 2) he’s family. 3) His big argument on his side is that he originally helped my partner buy the house, and they owned it together before my partner bought out his share. So his dad gains nothing from the sale. I understand why he could feel upset and also doesn’t want to lose all the things he left behind. But he’s also lived without this material stuff for years, has made zero effort to obtain it in UK, and now we’re expected to spend dozens of hours dealing with it while we’re trying to move. Every extra item if we were to take with us also costs me money because we’re paying by the amount we’re moving.

At this point I don’t want to help sell any of it or take any of it. I feel like if he wants to keep it he should pay for storage or hire someone to sell it or come back and deal with it himself.

WIBTA if I put my foot down and refused to sell any or take any more things with us?