Passport & Citizenship for Australian via FBR

[inphered]

Hey all,

I've search but either i'm not using the right terms or not seeing the answer, so I do apologise if this has been asked before.

I'll wanting to get my Irish citizenship and subsequently my passport based upon the Grandfather route.

My grandfather was born in Ireland, my dad was born in England before they moved to Australia. My father is a naturalized citizen of Australia and I'm 95% certain my grandfather didn't renounce his Irish citizenship but may have been naturalized. My understanding is that I can apply for my citizenship and passport, by registering my birth with the FBR due to my dad been an Irish citizen by birth, even though it was in England, due to his dad been an Irish citizen. I'm assuming his birth doesn't need to be on the FBR as he is automatically a citizen based on his fathers citizenship? This link been proven by the birth, marriage and death certificates of my grandfather, my fathers birth, naturalisation and marriage certificates and my certificates providing the links back to my grandfather?

Am I correct with my assumptions above, That the link of my father born in England to and Irish citizen, my grandfather, been enough?

Just wanting to avoid dropping a ton of cash if I can't get it due to my dad not been on the FBR if he was needed.