I'm an adult student, not a teacher, but figured I'd chime in anyway.
I’ve certainly been a beginner/tinkerer so I can guess a couple of things the husband might want/need.
First, I noticed that the OP said the request was from a parent, so presumably children in the family are already taking lessons. That tells me that the wife most likely understands that four lessons would be just a start. Possibly she is trying to support her husband’s musical interests … or hoping to convince him of the value of the paid lessons. Either way, it’s a great opportunity for the OP to meet a potential new student.
The husband may have specific desires/expectations for the lessons, so the simplest approach is to take some time at the first lesson to discuss what he hopes to accomplish in a month. Granted, his expectations may need adjusting, and the OP might not be able to prepare specific lesson plans, but that could be the easiest way to start. (Perhaps ask the wife to tell the husband to bring specific pieces to the first lesson if he wants to work on anything in particular.)
Beyond that, I expect it would be helpful to focus on reading sheet music, beginning with the most fundamental elements of key signature, time-signature, repeated sections, dynamics markings, pedal marks, how to count different time signatures, etc. (Counting out-loud, please! We beginners never know how useful that is until the teacher makes us do it.
) … and going on to intervallic reading, recognition of patterns, mnemonics for ledger lines, etc. Even if he's using lead books, or wants to play jazz, or really wants to learn the organ instead of piano so he can play at church ... Whatever the situation, knowing the basics can only help.
This may all seem a bit obvious to teachers, but I know from experience that beginners often don’t know what we don’t know, and it's all too easy to get hung up on reading the notes without stopping to consider/decipher the composer's overall intentions for a piece. I think that’s a key reason people find playing by ear so much easier than learning an unfamiliar piece from sheet music. They already know what the music is supposed to sound like and can keep adjusting their playing to match the tune in their head.
Just my thoughts. Hope it’s helpful.