We sure do have some very helpful members! I'm glad they have been working for you. They help so many people!
Usually you can tell them just like you spoke candidly here. They are aiming to assist you and would like nothing more than for you to guide them.
They need any details you can share such as the specific direction you wish to go in this case. Names, dates, marriages, locations... any clue you can hook them up with could be the one they need to unlock your family puzzle.
Best of all is to have a profile already created for the person with all known details and sources attached. Your G2G posts can then contain a link directly to the profile which makes it easier for the volunteers.
I hope this helps :)