I would just choose two names which I liked. I would go with names that I would use for siblings, but I wouldn't make them any more or less "matchy" because they are twins.
I think
Lewis and
Lois,
Molly and
Milly,
April and
Avril are far too similar. It would just cause to much confusion and would also make the child feel like the biggest part of their identity was the fact that they are a twin, rather than an individual. It's like when people dress identical twins in the same clothes - it's just confusing and means that the child doesn't have their own identity which is sad (and really annoying!)