Welcome back
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Her BRP expires 22 Jan 2023, so I think we can apply 28 days before, but this puts us at around 25th December I think earliest to apply, but will be after Xmas or in between Xmas and New Year to apply. Is this correct?
Yes, if she entered on a fiance visa and then switched to FLR(M), then she can apply up to 28 days before her visa expires on 22nd Jan 2023, which is 25th December 2022.
So, her application window will be 25th December 2022 to 22nd January 2022... and she can submit the online application at any time between those 2 dates.
So my next question is when do I start mail from? December 2020 to December 2022 or from June 25th 2020?
The mail needs to cover a MAXIMUM of 2 years, so it will be December 2020 to December 2022.
You will need 1 item of mail in each name, spread every 4 months, from at least 3 different official sources.
So, the mail will need to be from:
December 2020
April 2021
August 2021
December 2021
April 2022
August 2022
December 2022
All the mail must have been physically received in the mail in the months listed above. Online bills or statements cannot be used.
Also will it be the same FLR-M form I have to fill in online to extend or is it a different form?
It's the same FLR(M) form, as you are applying for exactly the same visa as last time:
https://www.gov.uk/government/publications/apply-to-extend-stay-in-the-uk-as-a-partner-or-dependent-child-form-flrm/apply-online-form-flr-mMy wife and I going to the US to visit her family for 10 days from Oct 5 to 15. Will this effect the visa or not?
Nope, it will not affect anything. As long as she is back in the UK in time to apply for FLR(M) in December/January, the US visit will have no bearing on anything.