OP, I read this thread last night and all the alarm bells it rang with me have been confirmed this morning by the additional information you've posted.
The reason you don't feel in control of this, or able to find a good way of maintaining the control you should have over what is happening to and around your DD, is because you actually don't know ANY of these people that well. Do you realise, you say upthread that you've only known the brother for two years - but the reason for that is that you've only known your own husband for the same amount of time, actually less if you met him when your DD was two and she's not even four yet?
What is happening here is that simply, you're only now at the point where you are really getting to know, from experience, what this family is like. The brother may be the biggest flashpoint here (and I think your instincts are spot on there) but it's just part of a much bigger and very worrying picture - of a really quite worryingly controlling family with some very strange 'norms' who have been quite successful so far in completely engulfing you in a pretty clever way. (You could even go further and say that you were an ideal target - you've alluded yourself to the subtle ways in which you find yourself in a position where you should be 'grateful' to have you, the single mum - and therefore your daughter - 'adopted' by this 'lovely' warm family...)
Only now, when you're more familiar, you've had more opportunities to see them up close, you're beginning to worry. And the problems start with your own relationship - if it were a case that your DH was more 'your outlook' with a weird family then you wouldn't be feeling like this as you'd be able to talk to him and have strategies for dealing with them. But - you didn't know him any better than you knew them when you jumped in and from everything you have posted he sounds pretty much cut from the same cloth. You describe a manipulator, a man whose instinct is to try and control, who you've needed to walk on eggshells around. Be careful. He knows when to back off and when to push, but as you get to know him better, you're seeing him more clearly. Do you really like what you see?
Two years is NOTHING.
This is why you need longer before really committing and this is what people have meant upthread about safeguarding with reference to your DH. Your DD was so tiny when you met him that the 'introduction' is neither here nor there - she won't remember a time before him, he is to all intents and purposes her father figure and always has been, it's not about attachment, and your DD sounds lovely and you sound totally on the ball with her. What folk are talking about is the wider picture of - is this guy really the lovely person he seems, can I trust that he, his family, his lifestyle, his values - are what I want for me and my daughter? When you married this guy, you simply did not know him or his family well enough to judge that and I think that you are now getting to that point based on first-hand experience.
My advice would be this. Firstly, to be absolutely blunt, I think that it is quite likely that you and your DH may split, and if I were you I would set out my stall now and not pussyfoot around. You have nothing to lose yet. You don't share a child. You haven't been together that long at all. Tell him how it's going to be, and fuck what his family think. Set out all the boundaries regarding his brother, your rules for YOUR dd now. His response will either be what you'd hope it would be, and he will shape up and get over himself, or you'll see the real him. And yes, tell him that in YOUR family, these are the rules. His family aren't more central than yours. Nobody has more of a say over your DD than you do. One of the most worrying aspects of your posts is your DH's immediate attempt to control here. He does - not sound great. At all.
Don't let him and his family softly manipulate you into buying into the narrative that you're the weak little incomer. Don't get sucked in further over the next couple of years, buying into the narrative that THEIR family are the core set of people, you're the addition, and they call the shots - it will just get so much harder to see the wood for the trees. Carve out your place in YOUR life now. If you can see that they won't let you do that - then for your DD's sake as well as yours - leave him.
Don't get pregnant. Whatever you do.
Don't give up your job.
Don't forget just how short a time you've really known any of these people.
Don't be afraid to open up to your family about how you feel - they will support you.