KOUYOUMJIAN comes from the Turkish 'kuyumcu', meaning jewelsmith. I'm told that my great-grandfather was a traveling jewelsmith in northern Turkey in the late 1800s.
OHANESSIAN is Armenian for 'son of John'.
JAMGOCHIAN is Armenian and Iranian: žamkoč‛, an occupational name for a muezzin, from žam, ‘church’, ‘mosque’ + koč‛- ‘call’. I've seen it defined as one who serves as a church caretaker or custodian.
Nancy