I think there was a pushy, obnoxious woman that was making their lives miserable. Can't remember who played her, but I think she was only on the episode where Charlie showed up. Bub was supposed to have moved to Ireland. Charlie, who was still in the Merchant Marines, showed up for a visit, and they ended up begging him to stay. I too was too young to remember Bub except in re-runs. We watched this show religiously until it went off the air, and Charlie is the one I remember and prefer. Every time I see William Fraley, I just think Fred Mertz.
Fedocia Barnett, played memorably by Reta Shaw, was the housekeeper between Bub and Charley. They could have gotten a few more episodes out of her - she was funny, and she played off the kids really well.