How can I help my Dad adjust to his new circumstances?

As an elder, although a bit younger than your Dad, this is my opinion. He has reason to be sad. He knows, as do you, that his life is ending, now as he knew it, soon in every way. Allow him to be sad, it is a difficult time, which almost all of us will share if we are fortunate to live long. Acknowledge it, it is no reflection on you. He wants to go home-to past life, activities, people, which of course seem rosier after we lose them. Try to understand how he sees it, let him talk about it, even if it is painful for you. He is already in pain. It may pass, it may not. Then ask him what he and you can do that my help. Something to keep him busier and distract him for a bit? Some old photos that allow him to weep? A shared cup of tea? A walk? Exercise is a great anti-depressant. Ask him to do something for your sake, let him be helpful to you and feel useful.

Anytime someone moves it can be very upsetting.
If you look at lists that list the most stressful events in our lives moving is pretty high on the list. If I recall it is close to the death of a loved one.
Give him time to adjust.
The fact that he has anxiety might not be helping.
Given his age there may be some cognitive decline as well and the "fear" of forgetting where things are, where you are can be stressful.
Is there a Senior Center or Adult Day care that he would be interested in going to to meet people, have some activity and be engaged with others? That might also help him

Time is your friend here. It takes a lot of it for older folks to adjust to change.

The one benefit to memory issues, if he has any, is that home will soon be where he is rather than where he was. Eventually it'll be where he grew up, but that's an entirely different issue.

If your father’s new surroundings include some of the possessions he enjoyed and activities he enjoyed and considered familiar in his previous living situation, you may have done all that’s possible to help him adjust, and in fairness, no matter what you and your husband have done, his “adjustment” may be

If he is able to continue with the medical services he used when he was on his own, those contacts may help him stay anchored as he attempts to reconcile his new life with what he’s lost.

If not, this may be a good time to help him connect with a comprehensive geriatric medical practice, that will give him, and you who love him, objective guidance when helping him through the inevitable changes that have begun to occur in his ability to manage his own life.

You have chosen to embark upon a new life for the three of you, and in fairness, you need to be ready to see unexpected changes and unanticipated reactions in each of you.

In a “perfect” elder care set up in my home, we realized in less than a year, that my mother, whom I had sworn would NEVER enter residential care, was unhappy and uncomfortable, and that the ebb and flow of life in a good local residence was what she needed to feel safe and loved.

I went every day for 5 1/2 years, and I too began to love what I saw happening for her.

I hope your situation develops into a pleasant, peaceful experience that meets one exceeds every expectation you have for the course you’ve chosen.

Whatever the outcome, you’ve clearly made your decisions based on the love and respect you have for your dad. That’s really one of the most important considerations when moving forward.

Please take care of yourselves, as you take care of him.

Create a consistent routine for your father. Ask him about what he misses from his former "home" and incorporate whatever you can. In a couple of weeks, the "new place" will feel like home.

The best thing would have been letting him stay in his own place, if he had the funds for Caregiving Help or Live In.
BUT, now that ya'll are all living together, hopefully you have brought all his old bedroom stuff to decorate his bedroom like his old one with the same furniture, pictures, ect.
Also, he should have the same chair that he always sits in.
It's very hard for an old person to make changes, especially if the person has a little dementia.

Just be kind, loving and patient with him and hopefully slowly but surely he can find happiness again in the new house.

But remember he is going through a huge loss and adjustment and it's hard at any age but very hard for Seniors this age.

You should deffiently explain to him why he needed to move and let him know you know how much he misses his old home and your sorry he is sad and assure him it will get a little better every day.

Imho, give it some time.