It's funny how English budgies are more expensive in other countries. Here the are the same cost and popularity.
I wouldn't recommend 2 English girls if you wish to breed. Imagine how hard it would be for the little male to mount a hen twice his size or more?
English/pet mixes usually involve pet hen and English cock. If they are not for breeding then 2 English girls would be fine
I wouldn't go back to same breeder for a hen with similar coloring unless the breeder is sure they wouldn't be related. Greywings are not rare mutations to answer that question.
If you were to pair up 2 birds with mutations like this you would get some normal grey wings and some dominant pied, sky blue and cobalt.