Not to seem cynical, but I'm afraid you picked the wrong company's product to help with your father's situation. Having gone through similar challenges with both of my parents (age-related dementia) before they died, I strongly empathize with you. The key is to either find a product that is either specifically designed for simplicity or one that is easily customizable. The Google line of products are neither. I am a retired software engineer, and regret the day I bought my Nest Minis thinking they would be a simple way to add speakers to my home streaming music network. The products are buggy, customer support is so completely useless as to be non-existent, and the company's sole focus seems to be on harvesting and profiting from the biometric data of their customers.
My suggestion would be to look into an Android tablet with cellular capabilities or maybe Facebook Messenger video, assuming you are looking to do video calling. If not, just a simple cell phone from one of the discount carriers would do. Just keep it simple and customize the device to your father's needs by removing any apps or features he doesn't need.
Anyway, good luck and I hope your Nest device is within the return period.
