Sounds like a pickle you’re in! But a fun one, without a doubt.
It’s great that you and your sister have similar styles, as that will help you when you need to consolidate or streamline your furniture or decide for the style of makeover you want.
If you want to keep all of the furniture in the room, my suggestion would be to paint it all the same color or same two colors. Choose a neutral shade or one that isn’t too far from your wall colors. For example if you have white walls, you could paint it white, pale pink, or some pieces each color! This will help make the furniture seem more intentional, which will be helpful since you described there being so much of it!
If you’re trying to give some of your older furniture a makeover, you should watch my series Upcycl’d! (Watch here: https://www.youtube.com/watch?v=agAs6F5VHcU) It’s all about how to take vintage furniture or pieces that don’t fit your style anymore and make them into new, modern masterpieces!
Good luck, Habiba! I hope this helps! Let me know how it comes out!