I was wondering if you could give me the correct pronounciation of our family name Ó
Macdha.

Gó raibh maith agat

Tá sé agat san fhoirm thraslitrithe cheana féin, a Mhéabha. You have it in the transliterate form already, with just some modification :

oh MOCKeh.

Giving its location, other terminations may have caused the -y ending.

Ceist eile is ea foirmeacha éagsúla tuisil, inscne srl., ach fágaimist siúd mar a táid. Bíonn blas ar an bheagán.

Ádh mór.