Myrna Shure: Part of the decision of whether to separate the twins is whether one is dependent on the other. If that is the case, you would want to wean the dependent twin slowly, maybe just a few minutes at a time, at first. Observe them and see how much the dependent twin can tolerate being away from the other.
If the twins are independent, treat them as any other children. Sometimes they would be in the same group, and sometimes they would not. Being a twin should not be the relevant issue as to which group they are in.
As for the language differences, this is probably not anything to worry about. If they are fraternal twins, differences in language are just like differences among other children. Unless it is a significant delay, I wouldn’t make an issue of it as it may only cause anxiety for the twin who is behind. If they are identical twins, and one is significantly behind, you might consider discussing this with their parents and suggest they ask their pediatrician for advice.