Normally, long distance diagnosis is difficult. In your case it isn't. Your engine is knackered. In case that is a UK word that doesn't translate, the engine is suffering from excessive wear.

I hope the great deal you got on the car leaves you enough cash to fund an engine rebuild, 'cos that's what you need. If you're lucky, the crank will be in good shape, but the cylinders/pistons certainly aren't.

There is a very, very slight chance that if the engine has been standing for a long time, the rings have seized in the grooves, but it sounds like all are affected equally, so this is unlikely.

In the UK you would have a reasonably strong legal case against the dealer.