You will be advised to keep all of your questions in one thread for the sake of continuity.
Assuming this is for FLR(M). It is not explicit in the rules (that I can find) that the co-habitation evidence must be from UK sources. However, I would recommend only using UK sources of evidence. As part of the application you and your spouse will be asked to sign a declaration authorising the Home Office to verify the personal information supplied (e.g. bank statements, utility bills, etc.). Foreign sources could conceivably refuse to comply with any inquiries made by the Home Office as it may not be done in accordance with local laws and therefore the documentation would not be verified and the application could be refused. Others may have a different experience/opinion though. The list of potential evidence you could supply from UK sources is rather long and the expectation for this type of visa is maintaining permanent residence and setting up life in the UK, which foreign sources of evidence would not support.
I'm just a guy on the Internet who immigrated to the UK. My opinions are based on my experience and interpretation of the immigration rules and should not be considered legal or immigration advice; your mileage may vary.