Kathryn I've just found your message. My great great aunt married a Thomas Mable (occasionally spelled Mabel) in Co. Antrim, N. Ireland in 1890. He was born in England c. 1841/2. Land records show Isabella Mable and Anne Mable as residents in the same townland. My guess is that Isabella was Thomas's mother and Anne his grandmother (or possibly aunt). I expect this is the same connection as yours. Mable is a very uncommon name in N. Ireland. Would it be possible that the whole family, with exception of Margaret, came to Ireland after Margaret's marriage and before your 3 went to PA? If Isabella was Thomas's mother, the 2 sisters you mentioned, Isabella and Mary, could have been living with her (so not listed in land records) or married and moved away. Do you have any more info - names, dates, etc., which could support this?