How do I look for adjacent objects instances of the same family in a grid?

You might need to create another family with the same objects. Then you will be able to use conditions like On Collision or Is Overlapping, for example:

Family1 is overlapping Family2 at offset -64

There are other ways of course. You can use another invisible sprite for detecting neighbors. But picking may be tricky. When one instance of the family is picked, you can't pick other family instances in the same event. So you will have to use "System Pick All" or do the overlapping checks in a separate function.