Our twins are 13 mos old tomorrow, and they have a lot of sharing time at the moment. We sometimes sit and pass a ball in a circle, handing off to the next person...S-h-a-r-i-n-g
However, if a squabble erupts about a toy while they play independently, they attempt to bite the grabby hand, or squawk loudly.
It's cute, but we try not to laugh, and promptly redirect to another toy.
We have sat back and watched as one baby just lets it go, and finds something new...it's amazing to us.
Lately we have separated them for short times (as they generally nap together now), Dad goes for a walk with one in a sling, and I stay and play with the other on our playfield...
They really seem to enjoy this, and play differently than if there is a brother to watch. Probably the same as napping separation.
I love this age... infact, DH just ycalled from the other room that he was getting teary eyed while babies were handing him toy "gifts"...such a mush.