I'm thinking of forcing my dad to be vegan as a condition of living in my home
Why would you force your dad to be vegan?
I've been a vegan for a long time and someone staying here should respect that
It's wrong to expect someone to adapt to your diet. You don't have to cook them anything but they should be allowed to eat what they buy outside at least.
I'll force myself to be Vegan if I only have to cook for two.
Not everyone wants to be vegan though. You can prepare vegan dishes for your family, but you should not expect them to adopt your lifestyle.