Would it be reasonable to assume that your parents have a strategy that has worked consistently in the past in dealing with you, that they can just kind of stall and things will blow over? Do you have a history of being assertive? Were the times that you were assertive in the past outbursts that leaked out of you, only for you to return to being more passive and subject to their desires?
If that is the case, perhaps it would be worthwhile for you to bring that up as a topic before you get to the other more pertinent issues that are bothering you. Stef did a show long ago with a caller talking about how his friends weren't responding well to the caller trying to expand the scope and depth of their friendship by introducing the types of content that FDR dealt with. Stef told the guy, "Well, of course not, you can't just change a relationship because the people had chosen the relationship that is pre-existing not the one you're trying to change to. At the very least, you need to explicitly state that you are trying to change the relationship so that they understand why you're talking about different things and put it in context."
So yeah, I think you've done a great job by pointing out that the reason you are talking about these things is so that you can improve the relationship and have it be meaningful. Kudos for that. Also, great on you for pointing out that you don't want to have a happy family dinner when they are not responding to the important issues you have been pressing them on for weeks first. Their natural response to that though would just be to dig in further and stall longer until they can placate you like they did in the past. So perhaps, go one step further and acknowledge your previous behaviours that allowed them to manipulate you, and point out that you are changing this about yourself, mentioning therapy and whatever else, and then make it clear that the stalling tactic isn't going to work, and it's only going to exacerbate the problems. I would also not accuse them of being conscious of the stalling tactic. The same way you would allow yourself to be placated to find peace in the home, and it just mutated itself into a habit in your mind, they could just have adopted the strategy without it being intentional or conscious. Like, it could manifest as nervousness or anxiety that causes them to withdraw, and then they find you placated after a withdrawal, which reinforces the behaviour of withdrawing to certain stress.
Anyways, I hope some of that is relevant to your circumstance, as I've kind of just assumed you were deficient in assertiveness before getting a response or confirmation.