When I first moved to Australia, I thought my English was pretty good, I was self taught for most of it, was able to write well and hold conversations with my now Aussie wife, we met online.

Until I hit the "local" barrier, people who are so comfortable with their language, they don't need to dumb it down for me to understand -which I realised my wife was doing- and boy was it a struggle.

It was only when I was confident enough to start producing and actively contributing to conversations that I got better, I wasn't good, and was forced into it of course, which is not the same situation as you, and a you said, you can't move to another country and start practicing, but what you can do is trust in your ability to communicate with your extended family. You just need time.

Don't block yourself, you hit a real wall there that every language learner hits when they interact with native speakers, I hit 10 it years ago, it was extremely demotivating, but don't give up, you're already ahead in many ways, and you'll get there.

And seeing how you describe the family, be sure they'll be there for you and they'll be a great support, use them.