You're comparing apples and pears. So they like this man, lets call him dad. They have a fantastic home life with a dedicated full time mum. You aren't in competition.
Each time they mention him do you scurry around making just a little more fuss? I used to do this, my kids are younger. I don't think they were trying to manipulate me or me pander to them. Time has helped. As has the recognition that in the early days I was so keen to not bad mouth I actually built him a pedestal so they actively tried to be nice about him.
Now we don't really talk that much about him. I have polite phrases like 'that's nice'. 'It makes me happy to see you happy'.
I also do things for me when they're at his. My children now appreciate more my world doesn't stop when they are out.
When they have exciting news to tell, feel sad or ill you are there and celebrate comiserate with them. You are their constant. Deep down they know that. They don't need it on the surface, if it is raised with them it risks them having to acknowledge that their dad has put this OW before them. That will hurt them not him. Something I know you don't want.
He has for what ever reason opted out of one of life's great journeys. Amongst the grunts and dirty laundry of teenagers there are still moments of wonder as you see them taking first steps into new pastures, showing their youthful vunerability growing and gaining independence.
On that note why are you doing all the cooking, washing and ironing? my mum and dad had us helping out from primary school age. One of us hoovered and cleaned the bathroom one did breakfast and we rotated. As we got older we cooked Saturday night and Sundays.
We even did ironing sometimes. I'm not saying we always did it well but it was a contribution and I think made us more ready for leaving home.
You don't sound selfish at all. I hope for you that you have just a little bit of you for you too. They are a very big part of your life but to be an interesting person you need a little bit of life too - I hope that you are getting it.
Venting is good.