A few things to consider before doing anything
Are you sure they are end-users?
Did the inquiries come via Sedo, Email, Godaddy, Broker??
Do you know who the companies are?
Have you check what the companies are worth?
Have you checked or done any research into what they have paid for names in the past?
All these factors come into play when deciding on who to sell a name to. Why sell a name to a startup with limited funds if you have a large company with deep pockets wanting the name too.