On balance,
Trump Sr. may calculate that if he pardons Junior, his lapdog Republican Congress will shield him from impeachment. The Trumps don't care how bad they look, as long as they escape the consequences of their actions.
Senior may well view pardoning Junior as just another cost of doing business, exactly like declaring bankruptcy. And just like bankruptcy, while normal people would be concerned about the damage to their reputations, the Trumps hold up even bankruptcy as proof of their business acumen. These are not normal people.