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So go with then 1st point and provide as much proof as you can.
any advice of which kind of proofs can we additionally give aside from:
*map locations, showing the 2 separate buildings.
*her auntie's letter of testimony and copy of tenancy contract
*her mother's testimony letter
*My Landlord's letter of testimony and his tenancy contract.
*pictures of the 2 buildings.
 
any advice of which kind of proofs can we additionally give aside from:
*map locations, showing the 2 separate buildings.
*her auntie's letter of testimony and copy of tenancy contract
*her mother's testimony letter
*My Landlord's letter of testimony and his tenancy contract.
*pictures of the 2 buildings.
Also, the some sort of address proof from municipality. Local councilor letter.

May be good idea to talk to some lawyer as well.
 
any advice of which kind of proofs can we additionally give aside from:
*map locations, showing the 2 separate buildings.
*her auntie's letter of testimony and copy of tenancy contract
*her mother's testimony letter
*My Landlord's letter of testimony and his tenancy contract.
*pictures of the 2 buildings.

There's a section in the application that lists proof of cohabitation, just use the same list to show that both of you had separate addresses, e.g. mail sent to you at that address, bank statements, etc.