, mama. Sorry, it sucks.
We go through this a lot still, but it seems to be getting a little better lately. In our house if one twin has something and the other wants it, I'll ask if the twin who has the item if she wants to share it. Usually I'll get a big old head shaking "no"
but I try. Then I'll try to divert the twin who wants the item's attention away and make a big deal about some other object. Usually her sister will drop the first item in question and they'll both get interested in the other thing (usually a book, or something they can both share).
Oh, and one of my girls is much better about sharing than the other. If she takes something from her sister, she almost always gives her something to replace the item--even without me asking.
If there's two of the same item and one twin has both of them, I'm a little more insistant that they share. I explain that she has two and sister has none and that she should share it. It's been working so far.
If they get in a knock-down-drag-out fight, then I just take the thing away completely and try to divert their attention away from it. I'm not sure how fair that is to the twin who had the item in the first place, but it tends to diffuse things a bit. Not sure how long that'll work either.
Good luck. You might find that they'll get better about sharing over time. I think mine are, but I may just be kidding myself.