similar to my previous experience, I didn't like BB to sleep on the bed of mother-in-law, thus I put a cover and claimed that it prevent baby to wet her bed, I felt much clean and less reject in this arrangement
My son started to climb from his crib and went into the helper's bed when he was 1.5 year old. I think his behaviour could be explained by the fact he played a lot with her on the bed during the day and before sleep, so when he got up at night he wanted to be close with somebody.
I finally moved my son away from her room, not that I mind her bed, but it was just too small for both of them. My son now sleeps with my husband in one room and I sleep with my younger bb in another room, so the helper get a room to herself with noone bother her at night.