It’s all in your head. Just say out loud to her, to them, that you are not ready for marriage yet. For you, being successful and settled doesn’t mean being a wife and a mother but achieving bigger heights in your career. Tell them that it’s okay if you could not give birth to any children but it’s not okay for you if you lost your motivation for life which is to do something big.
And tell them that it’s not your problem that your female cousins got married at a young age, it was their choice. Maybe their dreams were not as high as yours or for whatever reason they got married but that’s not your problem.
You have so many female friends and colleagues of yours who are unmarried and working hard to achieve their dreams and they are a better example for you rather than those two cousins who got married early.
Tell them that you have had enough of their bullshit. You respected them and thus you kept silent while they were trying through hook or crook to get you married.
And I don’t understand what your problem is. Why can’t you let me be me and do what makes me happy? I assure you I will marry one day when I am ready and I will have a happy ending but just to please you and others like you I can’t let my dreams die.
I hope you will understand this time and if you still don’t, don’t expect me to entertain your stupid demands anymore. Because from now on, I will not be silent.
And also just to remind you, I am an adult and I have all the rights in my life and if being pressurized I can seek help from the police too.