DD is 24 months. We still co-sleep and and nurse to sleep.
She has been away from me when she stayed overnight with her Mamma (my MIL) a few times this summer. MIL lives in another state, so when she is babysitting her because I am working, a sleepover can be worthwhile. We worked up to it gradually, over the course of the last year. We did this by visiting for the day, or with the whole family staying over, or having MIL stay over with us. DD refers to the bed in her own room as Mamma's bed.
DD has a good time with her Mamma, and doesn't seem upset by the sleepovers without me. My gut tells me that she is able to handle it well because we have a very secure attachment, and she is now becoming attached to her Mamma as well.
When DD is at Mamma's, they sleep in the same bed. When the whole family (DH, DD and I) stayed overnight at her house on Saturday, my MIL repeatedly offered to let DD sleep with her instead of us, but I wouldn't give up my snuggler despite having 3 of us in a full-size bed in the summer heat!
My own mother stayed with DD one weekend when we went to an out of town wedding. DD was 3 1/2 months at the time, and I pumped for a month before hand to get enough milk to leave for her. That whole thing was rediculous. I was engorged all weekend, and had to pump in a bathroom stall at the reception. In hindsite, I wish I'd taken my mother up on the idea of coming to the wedding with us, and getting her another a room at the hotel.