I suppose it is easier to think of a First Cause than to think of an endless series with no beginning. Maybe a few hang out together. A Necessary Being would be absolutely unlimited, because it is dependent on nothing outside itself. In a way. If there are two beings, they can't be absolutely the same, right.
Identical twins are two people.
Yes, but they aren't absolutely identical. There can't be two things that share all the same attributes. Then there would just be one. Something has to distinguish one from another. Well, it's actually kind of fun.