Hi OP.
Its really tricky I think. I was in a situation where I was the daughter (though not as dependant on my father as the daughter in your post I don't think!)
My mother left when I was about 15 (still in contact) and I stayed with my Dad in the family home. It was a horrible horrible time for us both and we were extremely close because of it.
He got a girlfriend about 2 years later who treated me awfully. I was made to feel like I had to ask permission to spend time with my Dad. She'd be angry if I was there having dinner with him and he hadn't told her I was going round (whilst she was at her home). Honestly it was bizarre, she treated me like I was some form of other woman.
I wasn't allowed to walk from the shower to my bedroom in my nighty 'because I was a woman and it's not right walking in front of a man like that'. He's my Dad!!! Bleugh.
The photos thing was also an issue. He didn't have them all over the house like your DP but he did have a collage in the living room of special moments i.e. my first baby photo, prom photos, 18th birthday etc... She told him it was 'like a shrine' to me and to take them down.
I could never mention my mum. Ever. It was like WW3 for my Dad if I did. And I'm not talking about me sitting and reminiscing about times as a family I'm talking about literally saying 'I went shopping with mum' when asked what I'd done that day.
In the end he finished things with her because of it. She made him feel like he had to choose between us and it tormented him so much.
Now I'm not saying you are anything like that but I would say to pick your battles. Your DP clearly loves his children and that isn't a bad thing. There will be things that get under your skin but please don't make your partner feel guilty for being close to his children.
There are obviously things in your OP which would annoy most people though i.e. constantly financially bailing them out. But honestly, it's his money. If that's what he wants to do then it's what he'll do I suppose. It's different if the finances are joint.