Linda will be 20 or 21 months when the new one gets here. Bobbie was 22.5 months when Linda was born. I didn't wean her until I got pregnant with this new one, just couldn't take the idea of tandem nursing through a pregnancy. And since she was only a week before her third birthday at the time, I felt OK with it. I'd wanted to nurse her til 3 anyway, & hope to go that long with Linda as well.
I was unable to stop myself from mooing a few times while nursing both girls, but that's just my strange sense of humor.
I did not always nurse Linda first. Sometimes I'd nurse Bobbie first, so I could make sure Linda got the hindmilk. Sometimes I'd nurse Bobbie first to take the edge off near-engorgement. I also nursed her pretty often in between nursings of Linda so I could get my supply up. Worked quite well.