Updating with same Apple ID

[Seabird8]

I have three iPhone 3gs. (P)primary and Apple ID holder, (M) minor (H) husband. We all shared the same Apple ID. Today I created a new apple ID for (H) phone and have NOT done the update yet. So now (P) and (M) share same ID. (M) did the OS5 update last night and everything went well. If (P) connects to ITunes to do the update, will (P) phone info be replaced by (M) info since we share same ID? Does (P) need a new ID to avoid losing personal info and having it replaced by (M) info? Since (H) has his own apple ID, is he good to update? Like how can I update these phones w/o losing personal info when you share the same apple ID? I know u can stop the sync but is that all there is to it when updating?