I think you will be okay, as long as you remove the members then add the new ones straight away. It's probebly set to the same day, you can ring up BAEC and get them to do if for you then it's their fault if it goes wrong.

They did just that when we changes the head of the HHA, both kids accounts got deleted all TP and Avios went, but after I had to create the kids new accounts under my name they managed to put everything back within 24 hours.