dont say even uff to your parents and dont unsettle them. And speak to them good speech (the way i understand it is "speech youd like to hear from someone else" ie the golden rule of love for your brother what you love for yourself) so if you have something to say to your parents that may improve their demeanour or what have you, please don't say it in a way you wouldn't like to be spoken to in.
If one is doing HARAM confirmed, then advise is good but if your parents are ordering YOU to do haram then of course you CAN not listen to them and disown them if it gets to a point where they are very insistent.
Giving your parents advice is very touching and hits the parent pretty hard and sticks forever.
So please make sure,if you want to do this, to brief them into how important this is and have them in a mood where they will listen and pay attention to what you're saying. If you have made a strict decision (e.g if they dont stop fighting everyday you will go live elsewhere) and there are ultimatums involved, be wise in letting them know the consequences of this conversation since it can affect the outcome (and income).
All that being said, one more PLEAAASSEEEE:
PLEAASEEE make sure you at least have some sort of idea what you're talking about (i would advise complete understanding before talking) and what it is, exactly, that you want to say.
What IS their problem. is it solvable? are you in above your height? can you help or will you make it worse?
their implications and effects on you. maybe they can go book a hotel room and have a boxing match away from you, i dont know, whatever works for you guys as long as everyone is happy with the decision.
if you know what you want to say and the outcomes you're looking at as your goal then it would be easier to communicate it.
list everything what you want to say in writing also helps.