Whatever he sent you in PM can't be too difficult, it's quite simple to set up variables like this. The Family becomes an object, instead of picking a single object you are picking from all the objects in the family. Pick random instance > sprite, or you use Pick random instance > family. If you're going to make a game with some complexity you should get your head around the debug mode and looking at objects to see what their current states and variables are, then you'll have an idea of what has changed and what is set as you expected.
As an example, you have ships. Ship A, Ship B and Ship C are all in a family called Ships.
Pick a random instance Ship A. That will choose one object, a randomly selected Ship A.
Pick a random instance Ships. That will choose one object, a randomly selected Ship A, Ship B or Ship C.
You select a Family as though it is just another object but really it represents all the objects within it.
They are useful for when you want to sometimes group events.
For example in this game, if you wanted to say :
Bullet A can damage Ship A
Bullet B can damage Ship A
Bullet A can damage Ship B
Bullet B can damage Ship B
You put the bullets into a bullets Family and the ships into a ships Family and then it becomes one event applied to all :
Bullets (family) can damage Ships (family)