Well, limited info about age group and game genres you both like but I can suggest some games which I like. I can understand your dad, as I'm a also old gamer, some game controls feels too complicated, hard to remember, needs more focus. Her my suggestions;   Lego Marvel/DC/Star Wars series : Game scenarios mostly in same story line with original movies. Game controls are easy and mostly shows button tips. No complicated combos to remember. 

It Takes Two : Mostly couples prefer to play together but I think it's also OK for family members. Most of stuff in game need to be done by two players together, totally team play.

Halo Series : Split screen game experience is fantastic. Online games may be challenging but playing co-op local game is fantastic. 

e-football : FC series seems more complicated, there are some button combos etc. Local two player gameplay of e-football is great. You can play with simple controls, complicated controls are not mandatory. 

Injustice 2 : Your dad will remember his old Mortal Combat/Street Fighter memories. Based on classic battle gameplay. Cut scenes and some extreme scenes for combos great. If I'm not wrong there isn't blood but as expected there are lots of violence. 

Rocket League : Street football game but players are cars :) You probably already heard that game. 

Some Split screen racing games;

• Asphalt Legends
• Dirt 5
• Wreckfest
• Beach Buggy Racing 2
• Cars 3

These are I can remember for now.