Not sure answer to your question above, however I have another one to add.

One of the household members of our group is my 96 year old grandmother in bad condition. I am thinking of removing her from the group and transfering all of her UR points to BA. If she is left in the group, BA Avios are taken out of all accounts in the group evenly for every reward. With 500k BA already, that will take us a while and her account will never empty, which we want to do as soon as possible after she passes.

Any issues removing her and then just using her account separately to book awards to drain the account faster, then maybe add her back once the balance is so low that we cannot use any miles for an award (i.e. under 4500-7500 miles)?