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.
Maybe you and I have different preferences in the different storage method tradeoffs. The reason I chose 2-of-3 multisig is redundancy i.e. fault tolerance. I can lose a key and still have access to the funds. In a 2-of-2 setup if I lose either key I lose the coins. The only way to have redundancy in that setup is to store multiple copies of both keys, but now you're talking about storing 4 keys instead of 3 in the 2-of-3 setup. Additionally, in the event I pass away and my family isn't sure how to recover the funds, unchained can assist them with the technical aspects. That isn't true for a home grown 2-of-2 setup.
Unchained will generate one key themselves.
I will generate two keys using separate devices.
I will choose a location to store a key and a family member will choose a location.
In this setup there are different key generation techniques used and different storage methods used and different geographic locations used. Redundancy.
I will likely be the only person moving funds, but I will be storing both my own funds and funds of family members, hence the desire to segregate the funds. I can sign transactions using the unchained key and my own key. The family member storing one key will also be able to do the same (e.g. if I'm incapacitated or unavailable or w/e) but they likely won't ever do this.
I'm not willing to trade away the redundancy provided by the 2-of-3 multisig setup, even if it means its harder or impossible to segregate funds. That said, I'm willing to listen to arguments for why my logic is flawed but so far I haven't seen any convincing arguments.