Not sure I can help you decide when to keep or not keep a given vehicle. That might depend on what you paid for it versus what it is currently worth on the market.
97,000 miles is not all that much for an engine that was maintained. Did your in-laws give you maintenance records? Perhaps if they had it serviced regularly at a dealer, that dealer will have a service record.
Lifter noise is generally attributable to dirt in the oil. If oil pressure is normal but the lifters won't pump up, something is clogged. A fresh oil change plus any number of additive products to free sticky lifters could solve the problem.
As for timing belts and tires, these are normal maintenance items, and with 97,000 miles, you are probably right at the replacement interval for the belt. Tires are worn out when they are worn out. That's something you should have noticed when you bought it.
So perhaps it is not as dire as you think. Pull the oil and be sure to use the right grade when refilling. I personally like full synthetic oil. Amsoil and Mobil 1 are good products. Be sure to change the filter with every oil change. If you add something for stuck lifters, such as Marvel Mystery Oil or any other such additive made for the purpose, be sure not to add more than recommended on the label so as not to overly dilute the oil. You can even add the additive to a running motor (idle) so that the additive is taken into the oil and main gallery a little at a time. Don't want to wash down the mains and rod bearings.
Ask your in-laws what they were using for oil and how often they changed oil (good maintenance in their mind might mean getting the car washed every week). Get any records they might have, if you can, and verify that service was performed as they said it was.
If possible, do oil changes yourself. I have never really trusted minute lube type shops. I have known guys to drive home with no lube in differentials, loose drain plugs, missing fill caps, and so on. Better to put in your own oil so you know what went in the engine.