@RampantIvy we all love our children I think and want to think the best of them, however when that desire prevents you from acknowledging who they really are, the good, the bad and the ugly, WE really let them down.
To be afraid of any sort of honesty in your relationship with your child fails them terribly.
No one will most likely ever be as wholly invested in your childs life success as you, their parent.
If you cannot be honest with them in kindness and respect, to warn them of peril and a poor long lasting decision, who will?
No one will.
Parents do it because we want the best possible life for our children and choosing a good partner is a huge part of that.
To allow a situation like this to limp on with the hope of gentle reinforcement of values to somehow wake this woman up is likely more hope than reality.
Parents denying who their children really are and colluding in the fantasy of them being obtuse or led astray by someone, does them a huge disservice.
No this would NEVER happen in our house because we both have boundaries, our children know we wouldn't tolerate it for a second.
The OP got caught up in a appalling situation at Christmas and instead of meeting it head on, she is going to limp on.
Her daughter is back 3 weeks later for round two............while mentioning her mortality.
I'm with @ZeldaWillTellYourFortune I wouldn't stand near him at the edge of a cliff and I'd be giving your daughter the side eye.........
I care enough about my children to be prepared to say honestly and with love, that Christmas was the most appalling invasion, intrusion and imposition and will NEVER happen again.
I would also being saying that OUR home is not for you to gift out to others.
A continuation of denial of some of your daughter's characteristics............
in her selfishness,
her disrespect of your home,
her conveniently ignoring you run ragged, her allowing his family to so completely abuse your hospitality,
to her now lack of reflection nor acknowledgement that they all were asked to leave,
to 3 weeks later pulling a stunt so he could return, ..................is all 100% going to come back and bite the OP massively on the arse.
I suspect your fear, denial and lack of confidence in your relationship with your daughter will lead you to a place of bitter regret, where you will sorely wish you could revisit this period of time and have dealt with her more firmly and decisively, modelling strong boundaries and self respect where you do not tolerate being treated like a skivvy in your own home by a bunch of ill bred opportunists.