It's tough, this time of year, finding a campground that's open. Those that are probably have just electric only facilities available due to the freezing weather. Rippling Stream, mentioned above, closes Nov 1.
According to their websites, the following private CG's have fhu in winter...
. It's about 10-15 minutes from Newark & 30 minutes to the N side of Columbus. It's a ways back from I-70, but might be the best for proximity to both of your relatives & your reunion.
Cross Creek Resort
. It's located about half way between Columbus & Delaware. It would be a longer drive to Newark (45-50 minutes) but shorter to the N side of Columbus (15-20 minutes). Plus it has easy access to a major state route (36/37) & I-71. There are several fast food restaurants & a Cracker Barrel at that interchange as well as Flying J & Pilot travel plazas.
Those are 2 CG's that I've been to that I would recommend. You can also check the Ohio Campground Owners Association
for other CG's that might be open this time of year.
There's only 1 State Park
that I think would do. It's practically across the street from Cross Creek. If you decide on Alum Creek SP, reserve electric only site A38 (if you don't have any pets). That's the longest site there. Even if the fhu sites there (only 3 of them) would be open (& I doubt they would be), they are only 20ft long.
If you need any further help, PM me & I'll be glad to check more places out for you. Safe travels & welcome back home!