Hello Welcome in H.C.M. I have gone through your query regarding excessive dryness in mouth with sticking of tongue to roof of mouth in sleeping hours. This clnical history of your father refer us to think about mouth breating and nasal obstruction during sleeping hours and in such cases there may be good snouring as well. Most likely your father is having thick and slack soft palate, there may be elongated uvula. My opinion is that get your father examined by ENT doctor for nasopharyngeal incompetancy in sleeping time along with sleep study. Your father may be made free from these problems but the corrective proceedure may be planed only after thorough examination and investigations. ENT doctors working for snouring may successfully handel your case. Regards.