3 pound Bailey tries to make herself tall.
4 pound Chile stays with her feet planted on the ground.
This is pretty normal behavior for each. They have distinct, individual personalities.

Bailey has never been trained to walk around on her hind legs. She just does it.
Chile has never tried to walk on her hind legs; despite watching Bella and Bailey do it all the time

BTW, Bailey's loss of coat this Summer is finally just starting to recover. That is why her hair is going in all different directions.
It was a brutally hot and wet Summer & September. Thanks, Climate Change. .