TWO is my vote, my two boys are from differant litters, a Maine Coon and a Selkirk Rex Variant which means that Ollie is TWICE the size of Stan two but they really love each other! It's great wtaching them and it was the best thing I ever did getting a second one. There is only 4 days between them in age but like I say Ollie is twice the size but Stan gives as good as he gets!
Can't imagine them not loving each other in years to come.