Dual national Spouse Visa extension Help

[Aslam0786]

Hi

I am a british citizen and my wife american passport holder is on spouse in the uk since 30 /09/15 and her visa expiring on 30-06-18.

i need a help regarding following questions please;

1- Spouse visa extension application will be under 2 year route or 5 year route category ?
2-she is have more then £16000 in her personal account so would she meet the financial requirement or do i still have to use my proof of earning showing more then £18500 in the form of salary slips?
3-i have claimed only my self HB for the small period of time so would that effect her spouse visa extension or ILR application in the future?
4- As a american citizen can she also eligible for british citizenship and if she can then would that effect her american citizenship ? and what is her best possible options available for her in terms of keeping both nationalities?
5- we just been blessed with our first child and i already applied and have the british passport for my baby girl but should i also apply for american passport as well for my baby girl. or if not then whats best option available for her to keep both nationalities?

Please help me to find these above mysteries as am really confused and cant find the authentic information and answers for these question, Thanks