Can I bring a number from another provider into a Family Plan, and are there name or ownership rules?

Yes.

First, the service needs to be ported to ALDI Mobile in the current owner’s name.
To add it to your Family Plan, the number must then be in the same name as the Family Plan owner, in line with ACMA rules. If it is in someone else’s name, they will need to complete a change of ownership or transfer first before you can invite that service into your Family Plan.