Re: twins fighting
Personally, that isn't something I would ignore. I would do what you are doing. Put them in time out. At 3.5, if after time out, they did it again, I would put them in time out and then separate them for a while. Tell one to play in one room and the other in another.
That said, my boys wrestle all the time. (My g/b twins don't get physical with each other, but my boy twin and his older brother do constantly and my 2.5 year old twins do get physical sometimes also with the influence of their older brothers) To me, wrestling is very different than actually hitting, slapping, or kicking each other. I do let them wrestle some, but when someone actually takes their hand and purposely hits the other (rather than just wrestling around on the floor), I stop them immediately and send whoever it was to their room. I don't tolerate hitting, slapping, biting, kicking or the like.
Heather SAHM to 6 who are 7 and under, including 2 sets of twins and our last little miracle, a surviving identical twin, born Oct 2012!