What you said about the good actresses that can't live their dreams is so true. Not always but often. The reason that is true is because people think that
If you haven't been able to convince them, there is a reason.
What is it?
Why haven't you been able to convince them?
I would guess that it is because you haven't been able to make your case. It's just like in court.
Imagine that there is a big trial. A man risks being found guilty of a terrible crime that he didn't commit. The defense attorny comes out and says to the jury, "You should believe us. My client is innocent." That's all he says.
The prosecuting attorney comes out to speak to the jury. She has facts about where the defendant was on the night of the crime. She has testimonials, witnesses and people who actually saw the defendant at the scene of the crime. She has DNA and experts come and testify.
Which lawyer do you think would be more likely to win the case? It's obvious.
The defense attorney must present proof, "beyond a shadow of a doubt", that their client is innocent. In order to be able to do his/her job, the defense attorney must do research. She/he must be very, very well prepared. They work long hours and they work really hard to present their case so that it will be compelling and credible. If they don't do that, they risk being defeated.
You must do the same. You are on the defense. The example might not be a case in which a terrible crime was committed, but the principles are the same and preparation is key!
Have a look at this page on my site for new and aspiring actors. It has 23 links to pages about different aspects of starting an acting career including two pages about how to convince your parents. One talks about the basic concept and what it will take to convince them. The second page actually tells you how to set up and conduct your communication and how to talk to them about what it is you want.