Selective ancestor veneration: Is it possible?

The answer is No.

It’s funny when people think they can exclude some ancestors from spiritual elevation. Sure, you can focus on certain individuals and only give offerings to them, but if you are doing ancestor veneration, you’re addressing them as a collective. Selecting only certain relatives is not ancestor veneration. They get to choose whether to help you or not, to help themselves in turn. You do not own them, you do not own the spiritual path of someone who is responsible for creating you, and yes, their spiritual path continues after death of the physical body. You are but a link in the chain of creation, and your own selfishness holds you back.