M.S.
I don't have twins but I have kids that are close in age 3 kids in 32 months. I tell my almost 3 year old that once her sister puts it down then she can have it. That is the rule if you put it down then it is fair game. My 3 year old will watch intently until her sister will set what she wants down and will go snatch it. My 18 month old is still learning this so I usually end up taking things away from her when she swipes things for her sister's hand or even the baby. She is really bad though at swiping so bad they call her swiper (from dora) at daycare. I am hoping she will learn things too. I try to point out to her when the older sister sets something down she wanted to go over and get it.