Hi - welcome... First off I understand your dad has been crazy busy for quite some time. I am not sure if there is animosity over this or just acceptance. I think your next actions may depend on how close you two are. Does he have someone else to help care for him? At 70 it will be a hard long haul if he doesn't no matter how healthy a 70 year old he is.

First off you need to find out if it is base of tongue cancer - or oral tongue cancer. Oral tongue is most often located inside the mouth, base of tongue in the throat. Most base of tongue (bot) cancers are HPV related - they do have a better prognosis because being a virus related cancer they respond better to radiation and chemo. It's because if this they don't always operate on this type of cancer.
If it is oral tongue usually the first line of treatment is surgery - then if necessary - chemoradiation -
Staging indicates the size of the tumor and involvement - the higher the stage the more involved the cancer is.
Usually the first three weeks of radiation are manageable, then after that it Gets progressively worse, until two weeks after treatment finishes, then its a slow climb out of that hole.
Most treatment lasts 6-7 weeks. And it's usually 3 chemos and 30-35 rads depending on the dr. And hospital.
I would call... Hugs.