If I read it right, this grandfather is your husband's ex's dad? Not your husband's father?  If that is the case, her father should be staying with her and not you and your husband.

Welcome! I am new too btw. I suffer from anxiety and am feeling anxious imagining myself in your situation! Did your husband discuss this with you beforehand? I feel like it is highly inappropriate for the father of ex wife to be in your house at all let alone spend the night. I would tell my husband this is inappropriate as I would like to keep our household private and not broadcast ourselves to the ex family. I also feel like it is asking too much of you as a wife to play host to someone you do not know. The home is our sanctuary. Also, it is a security issue. Is this man going to snoop for documents or steal something from the household? Since you have never met him you have not been able to assess his inner character. I would personally insist that he make other arrangements than in my home. 

I’m confused. Why doesn’t he visit the kids when they’re with his daughter and stay at her home? Not sure why he needs to stay at your place and in your home when the logical solution would be to visit his daughter & grandsons simultaneously? Unless BM has no visitation rights?

I’d create a boundary with DH that the moment any hostility arises, grandpa gets a hotel. If he can’t afford it that’s his issue, you don’t need to welcome a hostile individual into your home. Especially when the reasonable alternative would be for him to visit the boys on their mothers time. 

OH MY GOD! Hell no. There is no way on this entire planet that my DH's ex wife's father or any other person in her family would be allowed to step foot into my home, let alone stay with me.

I have anxiety reading your post. Why is this happening? If I were  you...I would go out of town while he is there....I would never want to see him or meet him....please make sure that this never ever happens again.

So your husband's ex father in law is staying in your home??

LMAO- No. Just no. Tell your husband no. no. NO.

He can get a hotel room to and is welcome to get the kids as much as he wants for the visit but no. No staying in the house.

This would definitely create some anxiety!

The hostile gene rarely skips a generation, or is a fluke.

Why can't he visit the kids when his daughter has them? Does she get them for visitation?

If it's not your husband's father, then he doesn't stay. Technically this man is not family. DH and kids can meet this man and go to the zoo, lunch, or whatever outing they wish to have together, but not under your roof.

Can I ask about the mean texts you've received from the Ex-wife? Why did you get them, and what did they say?

It's understandable that you feel anxiety, but I honestly think it's unlikely that her father will be the same. 

Personally I would not let this happen. If I was absolutely backed into a corner I would go away for the duration of the visit and just leave them all to it. I would stay at a hotel/motel or with a friend. Not my kids, not my ex-father in law, not my problem.

Let your partner deal with hosting him (everything from cleaning up the house, making up the spare bed to doing gorceries and coming up with entertaining ideas). Either it will be better because they can just all relax without you around and the father-in-law can focus on the kids or it will be awful and blow up in your partners face and he will realize what a mistake he made. Either way you can just avoid it all and take a mini break of your own. If you want to meet up for dinner or something then that is potentially reasonable if you are comfortable with it, but more than that and I would be busy with other plans.

I have met my husbands ex mother in law and she did seem more sane than the ex, but I met her for only a few minutes so I could not really say how I would cope if I had to live with her in my home for a few days. 

No!

My SS's GGF was the one to fly to our city to pick him up and take him back to SpermLand for SpermClan visitation.  This is the SpermIdiot's grandfather.  He was a nice man but we never extended an invitation for him to stay with us overnight before catching their flight back to SpermLand the next day.  SpermGrandHag asked but we never even blessed that request with any response other than "We will drop SS off at GGF's hotel 3 hours before their plane departs."  First, GGM would have taken the stance that though GGF was with the kid the day before travel, visitation did not start until the day of travel.  That is the kind of crap she liked to pull.  All kinds of manipulation and positioning that weasled some "win" for her.  So we never tolerated anything but complete compliance with the CO.

We would not do anything similar to what  your Skid's grandparent is proposing.  We did take my SS's GGF to lunch on several occassions on the day we were turning SS over to him.  We even paid for his lunch.  But we did not open our home or give up our time with SS.  GGF time with SS was on the visitation clock.

If this visit can't be avoided, I would do my level headed best to approach this with as much open mindedness as possible.

It is very likely that this woman's father is actually not like his daughter at all.  He may have zero knowledge of her behavior towards you and may be completely unaware of her vitriol.  She may keep that hidden so that her father doesn't think poorly of her. 

The fact that your DH would allow such a visit may signal that he had a positive relationship with this man and this man may very well have no ill will towards your husband and thinks his daughter caused the split.

I would try to figure out ways to be present.. but have obligations that may take you out of the way.. "so that they can enjoy their limited time together"