Alexander & Ann Somerville

hello, i am looking for more information on a gravestone in Slavin cemetary. i believe it was put there by my great great great grandfather Alexander Somerville for his wife Ann who was born 1800 and died 1835 (according to the gravestone). i believe these were the parents of my great great grandfather William who was i believe born in 1830 in Tyrone and died in Carrowkeel, Lisbellaw, Fermanagh in 1897. According to the Griffiths Valuation Alexander, Catherine (his 2nd wife?) and William (my gg grandfather) were living at Fassagh, Inishmacsaint, Fermanagh. Thomas Somerville is also mentioned at Church Hill, Inishmacsaint. Any information anyone can give will be greatly appreciated.