Gaffy, that was Melvin sister and yes she married Margaret Jane's brother.
The problem I had for years was that there were two Melvin kellys born in benraw, one 1841 the other 1847, both births then corresponded with the 1901 &1911 census. Parents for both were Margaret and John.
It wasn't until we discovered that one ended up in the U.S., that one was married to Margaret McCracken.
It's been no easy feat with this family and until the records came online it was all ifs and buts.
Though several years ago I accidentally came across a cracker of a will which linked Melvin with his brothers, from memory I think it was William Perry that registered his sister Margaret Jane's death.
Married a month shy of her 16th birthday and had went on to have 14 children, she died aged 42 in 1896