Hi,
I asked my girlfriend about this, as she did a lot of attachment parenting. The main thing she suggested was to night wean (this does NOT mean full weaning.. just at night)
Here are her thoughts.. I hope it was okay to share your question...
"Have kiddo sleep on the other side of dad so it goes, kid, dad, mom. That way, he doesn't have full access all night long. Once they can break him of the all night nursing, moving him to his own better should be easier.
If there is no dad sleeping in the bed, then she could put him in his new toddler bed, in his new room, and she can sleep on the floor next to the bed. She'll have to hear him whine and cry, but she's right there so it's different than CIO. Yeah he'll be mad, but mad is ok, at least he won't feel abandoned or scared. She could also try just holding him at night and rocking him when he wants to nurse. My AP friend did this and it took a couple of weeks, but it did work.
If she wants to continue to cosleep through this process and again, there is no dad sleeping right there, then she could wear something that makes it harder to just nurse right off the bat.
I think completely night weaning him is key, otherwise he'll get confused as to when it's ok to nurse and when it's not. This shouldn't affect his daytime nursing at all. If he does end up completely weaning on his own, then he was ready anyway. "
Good luck
L.