I've had mine four years, and have had a fair amount of issues with masks. Don't discount the level of discomfort he is experiencing if the mask or nasal tube is tubbing him raw. I tested a Liberty which covers the mouth and has two tubes up the nose. After the first night the inside of my nose was on fire, and i told my wife it had been raped by a band of marauding guinea pigs having a gang bang! I wouldn't want to inflict that on anyone!
OTOH, my issues mostly come from the high pressures I need - 22 inhale and 16 exhale where many people are less than 10. I have had to search for a mask is comfortable when tight, without too much bounce in the seal (some masks would bounce and scream when I inhaled), and with backing for the rubber seal all the way around.....without bridge support I get an air blast in my eyes. The one I have currently has a shelf under my chin which keeps the mask from riding up (one mask blocked my nose when it slid up, and 'taught' me to mouth breathe which gives 100% leakage) About all I can suggest is trying a bunch of different masks and trying to analyze the designs for what works for your Dad.
Does it ride up? Does the seal blow out? Does his face and mask need daily oil removal...washing?
Room temperature is a big issue if he doesn't have an air temperature thermostat....I get rainstorms and nearly drown if the room gets too cold, and toss and knock the mask out of position if I'm too hot.
Does the mask contour fit his face well enough that it doesn't need to be painfully tight?
Getting it to work well is a big deal. You can see the results when it works, and you will see it in lower blood pressure, energy, and general health. Keep trying!
Is your dad on medicare? If so, they are shortchanging him on necessary pillow sizes. I'm not sure about that particular mask, but mine, which is the swift fx for ladies, has pillows of various sizes. If there's a gap by the pillow it could be too small. Tightening the strap will help it seal, but make it uncomfortably tight on his head. Try getting other size pillows. If it doesn't work with that particular mask, try the fx swift for men. Alot of us use that here. That will also remove the situation with his nose being sore at the bridge if he uses pillows. One more thing. My father in law had walking pneumonia recently. Before he was hospitalized he became almost incoherent, not making sense, not even knowing who I am. Once he got treatment he was fine. He had oxygen loss and it mimicked alzheimer's <spelling, sorry> disease! He's fine now since we caught it early. Keep us posted. What a lucky Dad he is to have a guardian angel like you! Love, DJ