I didn't have all of those children at once, what I did was:

1. Take a screenshot of the family tree with just the husband and wife or existing kids and open it in my image editor

2. Paused and closed my game, then made a copy of my game's save files as a backup.

3. Opened the game, unpaused and tried for a baby. If it worked, I click on "Family" and then take a screenshot of the new child and add it to the family tree in my image editor.

4. Paused the game and opened up another family, paused that one too.

5. Copied my backup files and replaced my game's files. This will take the baby away so I can keep trying as many times as I want.

6. Repeated steps 3-5 until my family tree in my image editor is full!

I did this for my experiment, but you can use these steps to get the child you want, any husband/wife for your peep that you want and more. Just stop whenever you're happy with what you have and always keep backups in case something goes wrong with your little families.