Oh, oh, oh! Get Minnie and Angel!
We understand. Age, drugs…it all adds up. 
God, is THAT ever true. Aaron picked Dewey out because he laid so sweetly in his arms when he tried to pick him up - he seemed so laid back and unrufflable. We get him home and he’s into everything and doesn’t let us go to the bathroom without him. Then we get Eddles to keep him company and now he’s a henpecked mom. You never know!
Two things you must get, in addition to a litter box and a scratching post. One is Turbo Scratcher (your local Wallyworld will have them cheaper, I’m sure), the other is a laser pointer. Both of these things are for your amusement. The cats will go absolutely batshit over them, and you’ll have more fun than you can stand watching the cats. 
Oh yeah, I can totally vouch for the “different personality at the pound” thing. Heket didn’t mind being held while at the pound, at home, however, she squirms out of my grasp fairly quickly.
Sprinkle catnip over the TurboScratcher before setting it down. Replenish as needed. Enjoy the show.