I would say visit, it would be the kind and neighbourly thing to do. However if the man's OH is capable, then there's no reason for you to be gardening/shopping at all.
The only potential difficulty I see is the the visiting family already perceive you as having a greater role than you intend, so worth popping round to introduce yourself and say what you've been doing and its limits. They may need have conversation with the man in rehab to refer all his requests to his OH.
What did you you think you would have by your current age that you don't?
Govt announces Ukrainian style scheme to bring thousands more migrants to UK
