No, no, no, please do not use JS OOP!
I'm sorry, but there are some overly-eager participants in this forum - mostly kids I suspect - who always come up with the "use JS" answer, just because Snap! also supports expanding it with JS. But that's totally not the answer. I think we might have to introduce a teachers-only section in the forums at one point, so serious questions don't always get diluted by half-informed single-line "use JS" answers.
If you wish to access variables of another object you can use the OF block. Remember to first select the target object ("receiver") in the right input slot, then you'll see both that object's variables and it's custom blocks in the drop-down of the left input slot.
Is that what you were looking for?