Here's the FLR(M) form:-

https://www.gov.uk/government/upload...M_-12-2016.pdf

Here are few extracts:-

Applications on this form may be made online, by post or in person at one of our Premium
Service Centres. To apply in person, you must make an appointment.
If you apply by post, you must send your application to the following address:
Home Office
Leave to Remain - FLR(M)
PO Box 495
Durham
DH99 1WR
....... application forms change periodically. If you obtain this form some time before applying,
please check that it is still the version which must be used when you are ready to apply
Application for an extension of stay on the basis of your family life in the
UK as the partner or the dependent child of a person present and settled in the UK or as a partner or as the dependent child of a person with refugee leave
or humanitarian protection or as the dependent child of a person who has, or is at the same time applying for, limited leave to enter or remain as the partner
of a person present and settled in the UK and for a biometric immigration document
[QUOTE]
.......As part of your application you are required to enrol your biometric information. You will be charged an additional handling fee for this service, payable to the Post Office Ltd. You must pay the fee by cash or debit card when you attend Post Office Ltd to enrol your biometrics. Each dependant included on your application must also pay this fee when they enrol their biometric
information. Do not send the biometric enrolment fee with your application fee.

Slip look to section 8 of the FLR(M) application form on page 48 for the Application of Biometric residence permit


As part of your application you may be required to pay the Immigration Health Surcharge. Before
going any further, you should check https://www.gov.uk/healthcare-immigration-application to confirm if an Immigration Health Surcharge assessment is required as part of your application. You must complete this before submitting your application and enter the reference number in this
application.
..Where the applicant has to meet the minimum income threshold, the financial
requirement can be met in the following 5 ways:

- Income from salaried or non-salaried employment of the partner (and/or the applicant if they are in the UK with permission to work). This is referred to as
Category A or Category B, depending on the employment history. See section 5 of this guidance.
I've highlighted the key wording
Means you and your wife can use both incomes