Welcome Glassy to the forum.
Thanks for sharing your story.
I have bipolar but I know people who have unipolar mania.
Mania is very tricky as I loved my highs and it took me many years to realise they were far more damaging and destructive than my lows.
We associate behind sad and low with being ill so if one is very happy and manic it can be hard for that to be seen as an illness.
Does your brother overspend, take many risks, when he is manic.
When he is manic it will be very hard to talk to him so if you can find a time when he is not manic and is his usual self, you can try and work out how to help him when he is next high.
Does he manage to work while manic?
Feel free to post when you like.
You are not alone, and there is support here.