Why can't you just pick instances of sprites B with low fuel?
B fuel<10 -> B find path to yellow spot
If you want to differentiate objects in the family, the easiest way is to add another instance variable objectType to the family. When sprites are created, for sprites A set objectType="A", for sprites B set objectType="B".
Then you can do this:
Family objectType="B" -> Family find path to yellow spot
and Family fuel<10