Right, I read this comment yesterday just before turning off, but only now did I find the time to reply to it with the deserved care and attention. But first of all, let me tell you how sorry I feel about your brothers' childhood circumstances and also the distress that has caused you then and still now. But, like you said, understanding helps (even if a little).

As you know too well anxiety is linked to fear and the amygdala plays a central role there. The amygdala also plays an important part in consolidating and storing memories of stressful experiences. A part of it (the BLA) appears to be directly affected, following a stressful event, by a rise in glucocorticoid levels.

See, neuron in the amygdala of rats which underwent intense stress (through a controlled procedure that injected corticosterone in them) sprouted more dendrites, which caused them to display increased anxiety compared to the controls ^ref.. This suggests how trauma (or indeed PTSD) can result from traumatic events, and indicates how brain systems affect one another in times of stress.

All this to say that a hyperactive amygdala may contribute to the well-established vividness of emotionally significant memories ^ref.. It is no wonder why you feel the way you feel when a family member ins under threat :/ .

But, what drew my attention the most in your comment was when you said "this is worsening with age". Well, as you also know well, the automatic reaction such situations elicit just reinforce the neurobiological mechanisms underlying it. CBT proposes that a deliberate change in the thoughts (by rationalizing them) and the reactions these events prompt, would break some of these brain cell connections and form new ones elsewhere :)

I am so sorry @agmoore, I got absolutely carried away here. While writing to you (who I hold so dear), having my post-lunch coffee, and listening to some calming music.

I send you and your brothers bags and bags of love :*
I will leave you alone now :D