Ah, change is always a challenge :)
My own suggestion would be that if the second apartment is a workplace, an independent business, it should have its own insurance, the same way it will have its own utility bills for heating and lighting. The rent, insurance and utility bills should all be independent from your family home, not least because if anything happens at one property, it is contained and doesn't affect the other property. Of course, this means there has to be enough income from the second apartment or from some other supporting activity, after all your family bills are covered, to cover the costs of the second apartment.
You have talked before about a tension in your family about family needs and individual needs and I think this is common. I can only say it gets easier as you (and the relationship) gets older and things like jealousy become less important and, if things are good, disappear. Because everyone comes to understand what is important to them in the relationship, the underlying emotional security, for example, and stops worrying about things which are not exactly how they think they should be.
I'm sure it will all work out one way or another, and I understand it can be painful living through it, glad that writing has helped ❤️
Hi @shanibeer, both advices are really good ones. I see your point for the insurance. I thought about making one for me more like for formality but ja, you are right, it makes sense to split two apartments. I wish my family finds the way to get nicely mature and I think it's on its way :) I will see how it works!