If you are the only person with access to those coins and you are creating all the keys using the same wallet on the same machine and storing the seed phrases similarly, then there is no point in separating the coins and no point in using a multi-signature wallet for any of that.
You would only complicate things while giving yourself a false sense of additional security.

Your design only makes sense if the cosigners are different people.
That way you can have one master key and each family member having their own master key. Then you create a separate wallet for each of them using your key and their key in a 2-of-2 multi-sig type (your key + family member 1) (your key + family member 2) and so on.
This provides you with true additional security while truly separating the coins.