You have to be a JW for now???????
You believe it is a sin to pass the bread and wine???????
Okay. Answering the best I can while taking your thoughts into consideration:
You are only there for family apparently. You do not believe their nonsense. So consider their entire Memorial as invalid and do not partake. You are only skipping an invalid observance.
If you must insist that passing on the bread and wine is a sin, then make sure you are not in the seats during both parts. Go to the washroom or just stand in the back. When offered the glass or the plate, don't even touch it, just shake your head no. You have not passed. You just did not participate in their invalid observance. Even better would be to be seen at the beginning of the meeting and then slip out the door and go home before the passing of emblems. If you must be a JW, JW's will see you in attendance. Then you were covered. Or tell your people that you went to a different Memorial- and don't mention that you slipped out the door.
So many options beyond partaking and being labeled for that. Because if you must be a JW for someone else, partaking when that someone else thinks you should not- that is not helping your cause.