This statement makes
me sad. If it is true, your brother is an ass.
However, in terms of your juniper, the only thing you can do is to treat it like a newly collected tree with impaired roots. That means keep it in bright indirect lighting, high humidity, mist the foliage, and cut back on watering the soil almost completely. Treat it like a juniper cutting.
It's really hard to gift someone a bonsai and have them fall in love with the art form. It's like buying someone a mountain bike because you want them to go riding with you

If they liked the idea enough, they would buy their own bike. Then after a year you could buy them a nice hydration pack or some bike shoes

If people like the idea of bonsai enough, they can buy their own trees - or collect them - and then you can help them on the journey. I would never buy my wife a bonsai tree for this very reason. She just wouldn't be into it, and I would be creating an emotional liability for her - where she would feel if she didn't care for or love the tree, she would be hurting my feelings. She likes looking at my trees... and that's it. So make sure you are gifting bonsai for the right reasons - because the other person wants them, instead of because you want them to want them
Two days ago I was visiting a fellow tree lover. I brought him a tree as a gift. He was super excited. He gave me a cool landscape plant and a tree that he grew from a cutting he brought home from Japan. I am super excited. That's the way it's supposed to work