Welcome to the forum

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You DON'T need the following documents, so take them all out:
- Sponsorship Undertaking Form (not required for a spousal visa)
- Copy of sponsor's Passport including stamped pages (only the photo page is needed)
- Copy of ESTA
- sponsor's Original Long Form Birth Certificate
- 10 months of paystubs (only 6 months will be considered)
- Water bill as proof of address
- applicant: 12 Months of Bank Statements (cannot be considered)
- Charles Schwab Investment Statement (irrelevant to visa application)
To answer your questions:
- your husband's passport copy does not need to be certified.
- you do not need your husband's old passport anyway... it's irrelevant
- you really need a wet signature letter from the landlord giving you permission to live there - you might be okay with an emailed letter if it's the only thing you can get, but if you can get an original, that would be best (if you need to wait for it to arrive, you can always reschedule your biometrics... as you only have 5 days from biometrics to mail the documents to Sheffield. Also, if you needed to cancel the application for any reason, you can only get a refund if you have not yet attended biometrics)
- it's a good idea to include a content letter at the beginning listing the documents in the package
- No, if you meet Category A, you do NOT need to include any other categories. Savings will only be considered if they are above £16,000 and then on top of that you need 2.5 times the difference between his salary and £18,600, if he makes LESS than £18,600. Also, they must be immediately accessible in cash
- boarding passes are best, but if you don't have them you can use flight tickets
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So, a revised list of what you need (additions in red):
Applicant Documents- Settlement Priority processing receipt (if purchasing)- Printed online application
- Completed Appendix 2
- Stamped biometrics receipt
- IHS surcharge payment receipt- Current passport- Previous Passport
- U.S. Sized Passport Photos
- return shipping label (can be purchased from VFS GlobalSponsor Documents- Sponsor Cover Letter
- copy of sponsor's current passport photo page
FinancesMandatory-
6 full months (not 10 months) of original payslips showing at least £1,550 before tax on each one, the latest dated in the last 28 days
- 6 full months of original bank statements showing the deposit of every single payslips, the latest dated in the last 28 days
- Original Letter from Employer dated in the last 28 days
Optional but recommended- P60 Form April 2017
- original job contract
Accommodation- Tenancy Agreement
- original wet signature letter from landlord giving you permission to live there
Relationship- Marriage Certificate
(not marriage licence... the licence is what you get BEFORE you get married)- 3 Photographs (including one from wedding)
- Travel Confirmation emails for past 7 years
- Four physical cards from my Husband to me
- 7 Years worth of emails (including screenshot of all emails sent with subject and date)
(no more than 1-2 pages in total... just showing maybe 6 to 8 emails per year. No email content should be included)