I'm living in ireland with my american husband we are thinking of moving back wats the best way to go about becoming a citizen? Also my father lives in america for over 16 years legally. how could my sister go about gettin permenant residence.
Please help

first to become a citizen you must have lived with your husband in the usa for at least 3 years.
So the best thing to do is move to the usa by starting a green card application, which should be fairly quick (about 3 to 6 months sometimes less) if you re able to a direct consular filing in ireland.
Then you will be able after 3 years to apply for citizenship.You can read the article about getting citizenship in the practical advice section.

As per your sister and your dad. This relationship is not a "first degree" as husband and wife can be , so I believe she could apply but that it could take 5 years or more before it gets approved, if it does.
However, this site is specialized in hubsnad/wife situation so you might want to check with the uscis.gov website. The only official website on this subject.

Good luck!