I do feel for you. However, I really do think you need to take on board the experience of parents of twins who have been there and done that.
Generally speaking, multiples are going to have a harder start in life because they tend to arrive earlier. So a lot of these mums will know what they are talking about.
As the mum of a DC who has been at school with twins, I can tell you that the twins are generally lumped together by everyone else, whether you like it or not. I know I hesitate to invite one of the boys over without the other one, because although DS1 is more friendly with one of them, he is also friends with the other.
So having them in separate classes gives them at least a chance of not being lumped together all the time.
If your DS1 is distraught, and the school know that seeing your DS2 will calm him, they will likely bring them together occasionally anyway. They won't want to have a distressed child. But, it will be good for your DS1 to learn how to self calm, without relying on DS2's presence.
Also, it's hard for other children, who feel left out when friends with twins. I know my DS1 steered away from the twins in infant school because they were so frequently together. He never knew when one of them would wander off from him and leave him alone. They were in the same class. Yet now he is in a classroom with one twin brother (different school, different children) he is good friends with both boys, but better friends with one of them. So you may find that friendships with your boys will be more successful if they are in separate classes.