Thanks for sharing your concern.
In your case i will first suggest you to get his ridges examined properly,that is, if they are smooth enough to hold the denture?
there should be no sharp bony process,because howsoever good the denture is, if placed on a bony ridge will lead to stress
concentration in that area leading to inflammation and pain.
how long it has been since he got his teeth extracted?you have to give sufficient time for the alveolar ridge(on which the denture rests) to heal well and take a good rounded shape to bear the denture.
i would suggest you a revisit to your dentist
or second opinion
and further examination of ridges.
meanwhile practice gum massage
with your index finger regularly.also maintain good oral hygiene.
for further query you can contact me through my profile.