I'm so glad there's a thread here to talk about this, even if we're not tandem nursing (as of yet--i still have hope it could be a strike!).
Nursing aside, Nik (my 2yo) is mostly gentle to the baby, although in the first few days there were more than a few incidents of "pat, pat, smack!" and Nik pulling Ollie's head off my nipple while nursing, etc.
I guess it was naive of me to assume that Nik would just seamlessly transition to nursing with a baby around. He knew the baby was in my belly and would come out soon, and he talked excitedly about sharing milkies with him. He would say while nursing on one side that that was "his side" and he'd pat the other side and say "that one baby's". Maybe he thought that one boob would be exclusively his after the baby came??
He saw the birth and acted very daddy-clingy right afterward, and kind of mad at me Now he's back to his usual cheery self 95% of the time, except he's still not interested in nursing.
He has laid down in my lap multiple times, asked to have my shirt up, and "cuddled with the milkie". He's put his mouth up to nurse, and then looked at me and grinned, turning away. He says "baby milkie" and shakes his head, or tells me he's a big boy. However he's back to wearing diapers most of the time, instead of using the potty most of the time.
Arrgh...! Two weeks ago he was still my nursing baby, except I hardly had to change diapers. Now he's my big boy, acting all weaned, but OMG the diaper laundry is horrendous now!
One small bonus: My nipples are not sore at ALL this time, apparently since I nursed thru my whole pregnancy :) No more lanolin stains on my bras--yay!