I dealt with a case like this recently – pensions service had visited two pensioners living together and decided that they were a couple – raised the alarm bells, notified the LA, but 4 months later the alleged partner is still receiving Pension Credit at single rate. I went to see them myself and was satisfied that they were not LTAHAW.
I’d want to be sure of the quality of the home visit before I took the course of action you suggest – do they consider themselves to be a couple? Is there public achknowledgement that they are a couple? Do they share financial responsibilies in the home? Do they jointly own the property? Take holidays together? Share a bedroom? A lot of pensioners live together for companionship only. If your pensioners were both the same sex would you still consider them to be a couple?