mburton

I was born in England 1961. Parents and both sides of grandparents all born in England. Moved to US in 1984 on a B1 visa, that was converted to a permanent green card in 1994. Got married (in Stanton England - Westminster Abbey issued marriage certificate) in 1997 to an American lady (still married)...Two children June 1999 and June of 2002, just traveled to London for a week prior to Christmas on their US passports. Now trying to get them both British Passports.
I completed form MN1 (thinking that's what was needed) based on the Home Office web site. Then started filling out UKF form. Can anyone give me better guidance or direction please, so frustrated and trying to achieve before my daughter turns 18. What is the path of least resistance and what do I need to provide and to whom. Do I need to register them as British Citizens first, then apply for passport?

BritInParis

Your children are already British citizens. You just need to apply for their passports.

https://www.gov.uk/overseas-passports

Consular birth registration is optional but useful and worth considering.

British Consular Birth Registration : British Expat Wiki

HKG3

The OP should note that his children are British Citizens by descent. This means that they cannot automatically pass down their British Citizenship to their children (The OP's grandchildren) born overseas.