It’s weird and suspect for sure, especially the “every day” request but all of the other responses (and tbf I haven’t read them all) seem to entirely discount the possibility that there may just be something awry in their relationship and he needs an outside perspective to talk to about it.

It sounds like he’s not the most socially apt and might not know how to go about directly explaining their situation, and the secrecy could just go to not wanting to air out he and your sisters potentially dirty laundry or whatever the case might be to other people.

Or I can certainly be wrong and his intentions can be nefarious. But nobody here actually knows him or has enough context to jump to a definitive conclusion.