What are the best steps after a dementia patient attacks his spouse during the night?

alzhope16, have the family get Grandfather tested for an urinary tract infection because that can cause an elder to get aggressive.

I agree with Windyridge here. Unless it was an isolated incident, he needs professional care. We have an experienced CNA helping in our house at night.
Occasionally, we have these behavior problems that are very difficult
to manage at home.

Gramps needs to be in a memory care facility and get on some meds to control the aggression. Your inlaws will probably very quickly regret moving these folks in with them. It will be a 24/7 care detail.

Well, it does sound like they should not be alone, and moving them in may be the most immediate action possible. I agree the same bedroom is probably not safe.
Get Gramps to his doctor ASAP, if they cannot stableize him, it may be time for him to be in a facility that can meet his needs. He is not safe to himself or others if he wanders or attacks.
If you do not have extra bedrooms, you can always buy an inexpensive rollaway (or even rent one).
A very difficult conversation to have with either of them.
God Bless

They need to be separate to protect grandma. This often happens and many times leads to at least one of them moving to assisted living or memory care. If one of these places were to evaluate them and was told about the attacks they would not be able to be together in a facility either. Separate rooms in different areas of the building. This can be very serious. In my area just last year one memory care patient attacked another and ended up killing him. But, it sounds as if you have no control over the situation.

I'm not sure. :(

I agree with you that having them sleep in the same room isn't really addressing the issue.

Is Grandfather's doctor aware of this issue? What is the medical advice?