Most of the banks on the Lemonweir are privately owned. Even if they weren't there's a lot of old oxbows and wet bottom land down there. The high ground is not smooth and pretty heavily wooded. It's not what I'd look for for a group camp of any size, though solo or with one other perhaps it could be made to work OK. Lots of Cardinal Flowers along that river. (Its an especially great place to paddle for those who love seeing bright red flowers in all directions...) The last few miles flow through a marshy area that would be less than ideal for camping (due mostly to mosquitoes) anyhow. There is a good take-out at the base of a bluff on river right (but your left if you're paddling upstream from the Wisconsin) within a short paddle from the Wisconsin.
Your better bets for camping are out on the Wisconsin River proper. There's lots of sand (assuming the river goes down from its present spring flood stage) to camp on between the Dells and Portage. Just get your last camp in before the start of L. Wisconsin. (You were probably planning on taking out before that anyhow...) On that upper end of that lake and the area where it meets the river you may have to compete with motor boat campers for sites.
There's room for several cars at that Lemonweir take-out, but loads of parking at the city park in Portage. Perhaps dropping one car on the Lemonweir landing to use to run all the drivers to their cars at Portage? Mike Svob's book covers all the landings there about pretty well and there shouldn't be a lot of trouble working out a shuttle scheme.
Heel and Pegpads™
Kindle / iPad Cases
PFD's (Life Jackets)
Gedi Convertible Helmet