Is this move in doomed to fail?

I (43M) have been dating my girlfriend (45F) for just over 2 years. We are scheduled to move in together in 4 weeks and things are getting a little rocky. She has 3 kids from a previous marriage 2 of which still live at home. They are both boys 1 is 22 and the other 16. I have my own son I am bringing with as I have full custody of my 14 year old (only child).

1st we are moving into her house. Something I did not want to do, but financially that's what we can afford to do at the moment so here we are. We have been staying at her house for the past 2 months to save money for the move by cutting down on the back and forth driving and utilities at my place. She originally said that anything I wanted to upgrade or change she was open to. So the first few weeks I was like hey there is a lot of clutter here that we need to see about getting rid of or storing away. There are going to to be 5 people here now and with the few things I'm bringing it's going to add to the clutter and everyone was going to feel extra cramped. That was met with a flurry of why and disdain and out right negativity by her 16yo. I'm talking about board games and movies that hadn't been touched in over 5 years. Toddler like tantrum. I have a pool table I'm bringing, which he's cool with so long as I don't make any changes to the decor of the room it's going in. We had a new dishwasher installed as hers went out and he threw a fit about the one we picked saying it was too expensive we didn't need that one. The company that installed it damaged the countertop so we are getting new counter tops and a back splash. I asked of we could change the cabinet pulls as half of them are missing any way and I'm not a fan of gold. His response was "I like the gold, mom you like the gold, everyone like the gold but him why are we changing it". My response to her (in private) was he's not paying for it. Why does he get to tell us we can't change something. She said I didn't care about his feelings. I told her I felt like I was a guest here. She started crying saying I'm changing everything in her house that she put together for her boys. So I said fine. I'll put my stuff in storage and not bring anything and we can leave everything like you have it. She said I was being a child. So I suggested she let me know what she wanted to change and I would only change those things. She said she's already made a ton of changes (1 our bedroom we agreed to doing that together, 2 my sons new room). I tried asking if I could train her dogs and put them on a feeding schedule, as the house constantly smells like pee because she let's the dogs eat and drink all day and then when we are gone they use the restroom in the house. That was a huge fight. She says that I am calling all her stuff crap because I said I'd like to upgrade to nicer stuff, and wanting the dogs to not shit in the house. Am I making a mistake? Am I in the wrong.

Sorry for the long post.