I'll give a step by step.
1. Get a Mametchi, Memetchi, Kutchipatchi, or Furawatchi/Violetchi (I really don't care)
2. Find a Chantotchi, Mumutchi, Yonepatchi, or Sukatchi respectively.
3. Marry that tama with your equivelant ON YOUR TAMA. If you don't, it will not work.
The new tamas will be a varying number of pets.
4. Take care of the new babies as you normally would.
5. Don't freak out as the middle character skips to adult (your previous parent) and the sides skip to their younger sibling(s).
Example: Mame family
You get two eggs! They hatch into a boy and a girl. 1:30 later and you get: A Mametchi in the middle and a Chamametchi on the side! Yeah!
That's my example.