Evidence of continued relationship while living apart or outside the UK

This is on behalf of a friend who needs to provide evidence for the requirement "Evidence of continued relationship while living apart or outside the UK" for a dependant visa application.

Here's the situation:
He and his wife initially came to the UK together. He was the main applicant and she was on a dependant visa.
He later sent her to India for childbirth, where she stayed for about 5-6 months before returning to the UK with their child.
Recently, due to sponsor-related issues, he had to move back to India, while his wife secured a Tier 2 sponsorship at the same time and remained in the UK. Due to the delay in the visa processing, he went to India.
Now, he is applying as her dependant, and the checklist asks for evidence of a continued relationship during the time they were living apart or outside the UK.
When I searched online, it showed we can provide call logs or email exchanges as evidence. However, they didn't keep a detailed record.
Would it be acceptable to write a letter explaining the situation and attach some photos from their marriage or while in the UK (though not specifically from the period they were apart)? Would that be considered sufficient, or is there anything else that might help strengthen the case?
Any advice or experience would be appreciated. Thanks in advance!