Yep, need a title to get it registered with plates. You could try for just a bill of sale or use a bill of sale to then have a title made but I'm not sure what hoops you'll have to jump through. I think a moped can be registered with just a bill of sale but those are under 50cc and must have pedals.
2nd gen xterra would hit all points and be his best bet IMO. Real body on frame. Actually the same chassis as a full size Titan just reworked a bit. 270hp v6. Can tow over 5000lbs. Real 4x4 with locking diff (dana 44 on off-road models). You can even get one with a 6speed manual. You can fit a 33 inch tire under them without any real mods. 2nd gen started in 2006 or 7 but the facelift and little bugs were worked out by 2009.
I love all the guys on here telling him to go out with a friend with his family of 4. Sounds like you like the idea of boating. A simple outboard pontoon wont cost a ton to maintain like half these guys are stressing. It's no more than a "fun" car. Alum marina has rentals. Go rent one a few times this summer and take your kids to the Alum beach to see if lake water is what they like. I would say they are a bit young for it yet, but that's just me.
Go here and take the free boat training course and get your boaters license. Take your time and try to really learn about boat safety. Lots of idiots on the water.
https://elearning.boatus.org/
Here is an example of what I think is a good starter boat. Sea Ray is a great brand and it will be fun for the family and easy on fuel. Small size so you can learn how to handle a boat. Priced a bit high, I'd value it more around 8k.
https://columbus.craigslist.org/boa/4859641071.html
Used is good if you want your money back if you don't like it. I wouldn't go too old or too new mid 90s to mid 2000s seems to be the sweet spot. Maybe try a pontoon or a nice sized open bow. You really need to research and see whats best for you. Having no experience, I would highly suggest you make some boating friends like the handful of us on CR and try to pickup what you can. If it was me, I'd pick up a nice quality 18-20 foot open bow with v6 inboard power. How many girls do you have and how old are they? What do you have to tow with?
Alum Creek, Buckeye Lake, Indian Lake, Deer Creak, ect. Plenty of places to boat in central Ohio. Do you have a budget in mind? Do you have any boating experience?