You can send MS an email for #1 and #2. They will add the notes to each reservation. Just be specific and say “please add a note that reservation x is a continuation of the same group into reservation Y so please keep us in the same room. Have them do the same on the other trip too.
If you have points in your account just sitting in your account and some are banked, then modify your trip online, go through the motions but don’t change anything and rebook. It will take all the banked points first.
If you have more than one trip, then you may have to do it with each of them. Just do it starting with the soonest reservation.