When I look at the older thread, it almost sounds like the potentially maintenance-entitled persons are waiting for something to be gained....
Therefore, I would handle it in your place so that you are the sole owner, take out the loan alone, and they pay you rent. In the event of separation, only one person would be left with the debts, and she could not build any assets through ownership, but against this background, that would probably be the safest option.
Since the issue of parental support is one of the more opaque legal questions, I strongly recommend that you first seek legal advice here. How much assets is she really allowed to have before serious claims can be made? Once this question is clarified, you can move on.
Maybe then she can really be jointly liable and build assets "normally." If not, then it simply won’t be possible.
If she is allowed to have assets, but you don't want a 50/50 solution where she is registered in the land register and takes on the loan, your second step should be to consult a family lawyer for advice. There are "prenuptial-marriage contracts" that are similar to a marriage contract and can then be used as a marriage contract after the wedding. You will also get suggestions on how it can be cleanly resolved according to your ideas. We really don’t know what you want or what your specific situation is.