Hi Mr.Patil,
It's very common to have discoloration of teeth due to tobacco and bettle nut. Which can be treated by simply cleaning (Scaling).
As you said he is not able to chew food and considering the facts about the tobacco related habits which are risk factors for gum diseases.Gum disease treatment can be undertaken saving as many tooth possible and replacing the teeth lost with a permanent alternative. Ultimately he would be able to have food comfortably.
Next Steps
consult a periodontist and an oral implantologist for a comprehensive treatment solution
Health Tips
We at care dentaire have dedicated gum specialist and implantologist. Can effectively converse in English, Hindi, Marathi, Kannada & Telugu. Thank you. Hope my suggestions are helpful to you.