Question about employer & which catagerory to apply under

Hi everyone,

I have my biometrics appointment booked for 21st Jan 2018, & I just have 2 quick questions.

My wife works 40 hours each week & gets a fixed salary of £1332.64 net, a month and has been in this job since Feb 2018, under what category should we apply for? (this amount doesn't include any overtime or bonuses)

My wife works as a housekeeper in somebody's home and is employed by both the husband & wife.
The husband pays my wife her monthly salary but his wife is my wife's registered employer.

In the employment confirmation letter does she need both of her employers to sign the letter or just the lady who employs her as she is her registered employer? The man works away on business trips and is in the UK only 2 days a week and my wife is worried he wont be in the UK to sign and date the letter if he needs too.

Kindest regards,
Adriani