How about caring for them differently ;
for example, with one of your Tams, try to keep 2 Hungry hearts full and 2 hungry hearts empty as much as you can - all thru' their teens but keep the Happy hearts as full as poss all the time. Only play Jump until it is an adult.
then go for a different approach with the other Tam - keep the Hungry hearts as full as poss all thru' the teens, but keep the Happy hearts 2 full, 2 empty. Try to play at least 1 x Jump, 1 x Bump and 1 x Heading each day.
You are bound to get different characters!
These are just suggestions of course - you could try any variation on these!
Best, etc.
TamaMum