Can I hire a declutterer?

Yes you can. There are cleaning companies that do this but if you can't find one to offer this service see if one can do it but staggered over several weeks. The issue would be time if they don't offer this service as there's a worker shortage atm. If it turns out too expensive just put a call out on Facebook on a local page, there are people out there that love organising other people's homes believe it or not lol. A payrate between $25-$30 an hour sounds fair plus extra if you also expect them to drop off stuff to charity and the tip etc.