OK, you put a whole lot of explanation justifying your behavior… and when it really comes down to it, you embarrassed your SIL and her bf and then refused to apologize for it. What you did was extremely impolite; it’d be no different from someone stinking up the guest bathroom and then calling them out on it. You just don’t do these things. There was no reason to embarrass them as you did. Your husband had already taken care of the noise all you had to do was say “good morning, would you like some tea?”. But no, you chose differently.
All of the nonsense you’ve noted about SIL seems kind of normal for a young person. She doesn’t seem overly reckless or abusive. She isn’t actively harming you, she’s just living her life and maybe making a little more noise than you’d like on a quiet morning.
You’re right in that you are always going to be the +1 here. You married into this family, and while you are going to be the mother of the grandchild, your husband and SIL are your MIL and FILs children. They will always be the most important people to your MIL. And she will almost always come to their defense first. So if you want a close relationship with these people, then apologize.