OMG, Sharon, I'm howling with laughter--with you but not at you!
Unfortunately, we share this adventure. My Habibi kitty was owned by another family before I got her. The husband, my boss at the time, adored her and vice versa. The wife hated the cat. Each time my boss went on duty travel away from Kuwait, the wife kicked the cat out of the house. Didn't matter if it was raining or 130 degrees outside, the cat went out when the boss was gone. When he'd get home, he'd call Habibi and she come running home and back into the house. When they left, my boss swore on bended knee (really!!) he would send for Habibi once they got settled in the US if only I could watch her for a month or six weeks. So I agreed... But in the end, they never really tried to get her back. Habibi was a nut case at first...she howled all the time to go out. She lived under the couch or chair for weeks. If I'd had a place to put her, I would have...I had two senior felines waiting for me at my mom's house in WA. But eventually Habibi decided to be friendly--she was lonely I think. Fast forward to today...I have spent over two years getting her to fully trust me...I can cut the back nails, but can only get the occasional front claw before risking bites and scratches. She continually stalks the two old cats, causing them great angst.
And yet, she in two years, she has been one of the sweetest cats I've ever known. But ONLY ON HER TERMS! And either I accept that or we have no relationship.
She is a cute, smart, and PITA cat. I don't know how old Sam is, but cats can learn. He's obviously got cheap taste...all cats love the cheap food. Why? I dont know. I, like you, have spent a bunch of money on food no one will eat. My cats won't eat canned food of any variety. After finally finding a good quality food all three would eat for a few years, the old girls started to have gastro problems with it. Had to go through four different foods to find another one that everyone could/would eat. What a waste of good money. For now, we've found one (Royal Canin) everyone will eat and can tolerate for now. I've cleaned up more barf than I care to admit. Some were fur balls, most were not. Most were, "I ate too fast," "I don't like this anymore, " or "I can't tolerate this food anymore."
Give him time...keep "asking" him to interact with you. If he's not too old, he'll come around, but it takes time and patience on the hooman's part! Forcing a cat to do anything is impossible--hooman's always lose that battle! And while Sam smiles when you clean the litter box, mine like to wait til I walk away with the poop and pee clumps and then they jump right in again and use the clean box again!
REALLY? You had to wait until I cleaned it to jump back in??? REALLY???
Just remember, "Dogs have owners; Cats have staff..."