The partner awards seem to allow one open jaw OR one stopover. (I don't know specifically if this applies to BA).

Everything is the crappy new instant ticketing, so yes, the miles must be there.

I once made a partner award on BA. All was going so smoothly until.... (and this has happened with two AS agents) they don't realize that the connecting city (LHR) is the next day when you get there, so you will be booked, eg, 25JUL SFO/LHR and 25JUL LHR/XXX (which of course, needs to be the 26th). Then, of course, the flight wasn't available. Also, and I don't know if things have improved, there wasn't instant confirmation from BA even when AS showed availability. And so a couple days later, I received a "no go" call. It all worked out because I ended up going elsewhere on another airline and had a great trip.