yankeegirl wrote: Second, residing in Ireland (north or south) with Irish spouse will make me eligible for Irish citizenship after I think 5 years
As scrudu said, you can apply after 3 years (although clock only starts ticking when you get married and they won't count unlawful residence in NI). However bear in mind that processing times are long. 2-3 years to process a naturalisation application and with the huge increase in the pool of eligible persons in the Republic of Ireland, that's not likely to improve anytime soon.
Equivalent processing times for British naturalisation are 4-6 months.
The other possible complication with Irish naturalisation is that the "discretionary" aspect is much less well understood compared to the case in the United Kingdom. British naturalisation is technically discretionary but cannot be refused on the whim of a minister or public servant - there are established policies which must be respected in taking decisions.
There is of course no reason why you could not seek both citizenships, as the law does allow this.
and would be easier if I just obtained Irish citizenship as both partner and daughter are Irish citizens.
Also bear in mind that if you choose to live in the United Kingdom as an Irish citizen but not a British citizen, you're a very welcome guest - but that's about it. It's not your country, basically.
How long has your future husband lived in the United Kingdom? After 5 years he is eligible to apply for naturalisation as a British citizen if he wishes. After then you would be able to access the shorter waiting period for the spouse of a British citizen. However you would still need to have UK permanent resident status.
My daughter was born April 2005 in Northern Ireland.
You need to know that children born in the United Kingdom to resident Irish citizens are normally automatic British citizens (at birth). However, as she was born before 1 July 2006 and you are not legally married, she probably did not acquire British citizenship at birth based on her father's status.
That said, once you get married, she should
immediately acquire British citizenship on that basis. I would not expect front-line UK Passport Office officials to necessarily understand the law in a case like this, so you should (after you get married) write to the Home Office Immigration & Nationality Directorate in Liverpool and ask for a letter confirming her British citizenship by virtue of sections 1(1)(b) and 47 of the British Nationality Act 1981.
In fact, if her father's "domicile" was still in the Republic of Ireland when she was born, and if Irish law has abolished the concept of illegitimacy (as opposed to just its consequences), then she may be British already. However if you're planning to get married anyway, just write to the Home Office IND afterwards and see what they say.
Have you obtained confirmation of her US citizenship and obtained a Consular Report of Birth Abroad together with a US passport for her?