Add objects to family from events or idea for sliding menu?

I am not sure I understand your question. You need to add all objects to a family in the editor, you can't do it in runtime. Same objects can be members of multiple families. For example, if you have the same button in a vertical and horizontal menus, you can add it to two families - VMenu and HMenu.

Also, check out this demo:

howtoconstructdemos.com/scrolling-a-list-of-players-scores-images-etc-example-a-capx

I need each of these buttons to be slideable. The day, month, year etc. .

The problem I have with the family system inside the editor is that this way I would need to make one separate object for each button and can not use my ButtonCreation function.

That's a pity that it can not be changed in runtime.

Edit: Thanks for the demo though. It helped me with another problem. :D