How to purchase a home for our daughter?

Our daughter is 34, unmarried (living with 42 year old boyfriend) and they have 1 child. My biggest worry is that they are still renting, unmarried and her future as far as a roof over her head. I'm suddenly thinking of the day when my husband and I pass and I want to make sure our girls are all ok.

We have the money to help her, but I don't know the best way to do this. I obviously need to protect her (and us) and not let him be able to take this home from her in the future - very important! She will not qualify for a mortgage on her own but she would be able to make the payments. They both make good money, work hard but have no financial sense at all.

My first idea would be for us to purchase a home where they live under our name and they pay us rent with a signed lease. How would this work when we pass away? We have two other daughters and we would need to keep this fair so that one daughter doesn't receive more than the other.

To round this up here are my specific questions:

How does this work with taxes as far as us purchasing another home?

How do we keep him from having any ownership of this home later on (may not be possible if they end up getting married)?

Any other legal advice?

Thanks.

EDIT: I've decided not to do this. I came up with this idea (as I said in my comments) on a sleepless night and I just came on here to get some ideas. Boy did I get them! I would never take legal advice on Reddit, but it did help to "get my ideas sorted out". We are meeting with our estate attorney soon to sort out the rest of our estate and this was just one idea I had. No, this is not a control thing. I just want to know that my daughter and granddaughter have a roof over their head. She works hard, and is not a "total loser" as it seems. She has zero debt except for her car (he has a ton) and she did just pay off her student loan. She just can't get ahead and doesn't understand the importance of saving for retirement, a down payment, etc. We are also offering (they have to accept the offer) for them to meet with our financial planner. If they have someone they want to use, great! They just need a reality check of where they are in life and what is coming up. We are starting a 529 plan for our granddaughter (also going to talk to our attorney re: the best way to do this). Also, we will treat all 3 girls fairly - 100%.