Yes, asking a random Rabbi you don't know to take on an extensive research project for you would be a little rude, I agree. So, instead of asking random genealogy buffs, try posting on JewishGen (you'll get a much larger response) for recommendations for researchers in Israel who will do this for you for a fee? My cousin would probably respond as he lives in Israel, is completely bilingual, and does this sort of work. If not him, then there certainly will be others. If you have a budget, by all means mention it so that only the folks who are sure they can stay within it will respond.
Finding a living family to reach out to is a lovely project and I'm sure plenty of people would love to help your friends by helping you out. But you're talking about 10, 20, 30 or more hours of work. If you're super lucky, it might be half an hour, but chances are you're looking for Sonia's children or grandchildren, not her.