Mentally unwell sibling and visiting family

My sibling is mentally unwell. I have bipolar and so did one of our parents, insure of any more family members with it but I know the signs, behaviours and with a small family history, I believe my sibling is also bipolar. Sadly, their behaviour has caused another sibling and I to avoid them, but because of this, we never see our other parent as this sibling moved in to help "sort their life out"
They are explosive, extremely short fused. They have used drugs, to self medicate. They are over the top in opinions, talks over us all, to the point they are almost blue in the face from constant talking. They partake in risky things, and drinks every single day. When they talk, it becomes like, stimulation, uncontrollable dribble of irrelevant topics. They sleep all day but can also just act manic. My sibling has been like this since a teen, and can get violent at times. Our other parent can't understand why we avoid visiting, we want to visit in other places but it's not good enough. How do we handle this