I'm not sure if there is any truth to this but it was definately the case in my house.
My RB Jock was defo a mummys boy and his sis Bonnie loves her daddy to pieces. Thats why when Jock passed away I found it sooooooo hard as I was pretty jealous of Bonnies relationship with my boyfriend (I know its silly but I couldn't help it!!). Anyway luckily for me Bonnie divides her time equally between us now