Congratulations on your move to the UK and your wedding

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* We just rented a flat which is managed by an agency (so we don't know the landlord in person), we both have our names in the current tenancy agreement. In this case, what would I need to provide for accommodation section?. I was planning to submit a copy of the tenancy agreement since I don't have the original one. I am not sure whether I need as well the land registry or any letter from the landlord giving me permission to stay in the flat.
If you are both named on the tenancy, then all you need for the accommodation is the tenancy agreement. A letter from the landlord is only required if the visa applicant is NOT named on the tenancy.
Ideally you need the original tenancy agreement, though if the copy is what you were given as being 'original' it might be okay.
* My second question is about the relationship evidence. It says that we need some letters from the bank or bill services along two years sent to our address with both names on it and others with only my name and her name. So, of course, we haven't lived together long enough to satisfy this requirement. At the moment we have a council tax bill with our names on it. A document that we opened a joint account at the bank last week. A first internet service bill with my name on it and the electricity and gas with her name on it. Should we submit the same documents we did for the fiance visa again? (photos, flight tickets, train tickets, Whatsapp conversations)
No, for this visa you DO NOT need the same documents as for the fiance visa, because you live together now... so you don't need to prove you are in a long-distance relationship anymore.
Instead, what you need is:
- marriage certificate
- a photo of you together (if you are applying by post... not needed for an in-person app as you will both be there at the appointment)
- your 6 letters addressed to both of you at the same address in the UK
As you have only recently arrived and may not have been able to get 6 letters yet, you just need to provide as many as you can and then explain in a letter the reason why you can't provide 6 items each.