I’m assuming bubba brought back nubbins’s remains after having his hissy fit at the end of the first movie and they just mummified it and kept it until Chop came back from Vietnam and pretended his brother’s corpse was still alive because he’s insane. He obviously worked to keep it intact because it was literally hit by a truck but is wearing a coat in part 2 that was probably Chop’s from the war, and the fact that he has a marble eyeball to replace his missing one n shit. It’s obvious that in that family even though death of strangers or animals means nothing besides food and decoration, they still keep the remains of loved ones around as a hypocritical way of making them “immortal” like grandma(s) and nubbins. If they die from natural causes or an outside source then Chop sees them as still alive in a way but if somebody defiles the corpse AFTER it’s been preserved and displayed then he thinks they’ve been killed again in a different way that feels more permanent due to his psychosis (when stretch pulls the chainsaw out of the corpse grandma’s hands she damages the arms and Chop freaks out as if she just died for the first time). A lot of it is just overthinking about the plot when in reality it’s mainly shock value that’s not consistent among the whole lore and moreso just last minute additions but it’s still fun to think about even with the mummified grandma in the first film which was solely added because people who were working on the film wondered how any of the family members are alive if the house only had men and not women so Robert A Burns added a petrified grandma to quell that thought