If you look at photos of Jeremy´s biological family, you see a bunch of fun loving, humorous people who don´t seem to take themselves too seriously. Probably Jeremy has that in his genes, but that wouldn´t have fit too well with down to earth, hard working, religious country folk.
We know he was a prankster, and that it didn´t always sit well with the family. He would have had to suppress some things that came naturally to him. Same with Sheila probably, but perhaps some other qualities, like being more openly affectionate for one.