AITA for not letting the former owner stay in our new house?

My partner and I are in the process of buying our first home. Everything has been arranged with a fixed settlement date just before Easter. We have booked movers for the day after settlement, given our landlord notice, and made plans for family to come over for Easter to have lunch with us and see the house.

Today, less than two weeks out from the settlement date, the seller has contacted us saying they want to stay on for up to 5 additional days in the house (paying us rent for that time), as a house they're buying won't let them move in early. AITA for saying no? 5 additional days would wreck our moving/Easter plans and it's not our fault that the seller hasn't properly arranged for alternate accommodation ahead of time.