We want to go from SFO to Dulles, drop off kids with family, then husband and I go on to London for holiday. If we book the entire flight. (SFO-iAd-Lon) through BA, it is about $600 cheaper for me and $600 cheaper for my husband than booking as two separate flights (SFO to Dulles, and then Dulles to London - I suspect bc BA allows stopovers). However, I can't figure out how to add the two kids' tickets. They aren't coming to London, and I can't buy a BA flight from just SFO to Dulles (website says BA isn't authorized to sell tickets with this routing).

If I buy the BA tickets for me and husband, and then buy the two kids tickets on American (the SFO to Dulles segments are on American), then 1) how do I avoid unaccompanied minor fees (since the kids will be with us, not unaccompanied) and 2) can I link the PNRs somehow (ours booked through BA, the kids booked through AA) to avoid being separated in the event of a rerouting? Or any other ideas how to do this? Will BA let me buy just the segments I need kids and more segments for me and husband? I'm confused!