The first one is 500,000 poly's, GTA IV will never be able to run that. It would take way more than just converting it to get it in game. You'd have to take the poly's from 500K to under 50,000 to even think about getting it in game, almost impossible. Your probably better off to pay someone to scratch make it.
The second one is a little better, that only comes in at 119,000 but still needs to be reduced
The third only 39,000 which is more on the GTA IV level
Good luck finding someone to convert them and I wish you even more luck finding someone to reduce them, especially the first one