I think the slight sound variations on the names makes it feasible. The
BETH of
Bethany is much more pronounced, for me, than the -beth of
Elizabeth (which is more like "Elizibith"). So it could work... as long as they both don't end up as
Beth, as itsnotmykitchen says!
Elly and
Beth would be darling, or
Liza and
Beth. Beautiful combos!