rother: Br`athair (bra-hair, but the H is almost silent)
Sister: Piuthar (Pyu-har)
Mother: M`athair
Father: Dadaidh, athair (its more polite to say athair)
Granny: Seanmhair (often said shen-a-vair)
Grandpa: Seanair
Cousin: Co-Ogha, Ciosan (but that also means a basket of bread)
Aunt/Uncle: Just say brother/sister of my mother/father.
Piuthar m`athair for aunt on mothers side.
Note, it can be more polite to put an a in between the words and turn the m`athair into a mh`athair so:
Piuthair a mh`athair (pyu-har ah va-hair).
This is a general way to make thing more polite.