Is it OK for you to bring up good memories of Avi?

Yes, whether at Shabbat dinners, chance encounters, etc. I find it comforting when somebody brings up Avi in conversation, whether about recollections or simply how much he is missed.

Also, I, myself, won't be bothered at all if you had a child in Avi's class or group, and you mention what your child is now doing or has achieved. However, I write only for myself. I understand from other bereaved parents that they would have different, less positive, reactions.