Do you have, or know of, a realtor in that area with whom you would list the property? I would contact a realtor and see if that person (or agency) knows of a short-term property manager you could use (ideally within the same firm - many realtors do provide this). In my experience, realtors are really well connected with home repair services, painters, septic pumping companies, landscapers, and so on. Get an appraisal of the property as well as recommendations on what you need to do to spruce it up to get it market-ready (tell them your budget, of course, and ask what the best use of that budget would be, to get you the most bang for the buck). Let the tenants know that someone will be coming in to assess the situation, and of course give them notice that you anticipate putting it on the market. Depending on when their lease is up, you can either have them leave, or go on a month-to-month lease until the property is sold, if they are willing/interested.
Then let your manager know that you no longer require his services as of X date (put it in a letter, return receipt/certified so it's signed for), and that you will be putting the home on the market. Let him know that you are consolidating short-term property management with a real estate company just for efficiency's sake - say "it's included" if you want to. Obviously his days of managing the property are numbered anyway, and this way you don't have to confront all the shortcomings. (Of course, if he asks for a reference for other people, don't do it!) Put in a brief paragraph reminding him that you are waiting for ABC paperwork, essential for doing your taxes, and that you will send him his final paycheck when everything is received. Make whatever arrangements are necessary to get the keys back, and let the tenants know whom they should call for repairs after the specific date. (And DO NOT send a check until you have everything you need. If you have to, get an extension on your taxes - it's a pain (especially if you are likely to get a refund), but it's legal and will buy you the time you need to get everything done.
You can still remain friends with the wife, and through her, the husband - for now it will be a long-distance relationship anyway because you live so far away. So you can have cheerful phone conversations and exchange newsy letters, and put this unsatisfactory business relationship behind you. If questioned, you can say how much you value the friendship, and now that they are married, it might have been better for BOTH sides if there were no professional relationship, but since you are selling the house anyway, the business association would have been ending anyway.
Very nice of you to value the friendship and want to keep it.