Has anyone experienced breakdown of sibling relations?

Your brother flips out because your husband is getting the septic system fixed? His reaction is odd. He should be relieved you and your husband can resolve this emergency. For the safety of your mother: Your brother needs a wellness check.

Call the Area on Aging and ask them to make a visit to check on mom and brother. Does your brother have POA? Perhaps its time to file for guardianship. He sounds unstable.

Being an only child this has not arisen. How ever my mom has 3 siblings. One told me. " Hey, you are on your own kid". The other told me he never wants to see her in a home and will do everything he can to prevent it. The other said to call her when I need to talk. All live out of state. When I told my uncle I'm one person who can't be 3 8 hour shifts of nurses every day. He said. Ok. Let me know when you and your husband need a break , and " if we can". My wife and I will come up and stay. Really ?? That's great. So we will see. It is on me 24/ 7. I kind of prefer the honesty of the aunt , who said. Hey it's all on you kid. Because it is

let me be clear:
i spend one week a month at mom's house. we were in agreement that she should have in-home care and suddenly that was "off limits'.
There was a big fight when my husband and i went down to visit for a week and found out that the septic system was disconnected... yes... as in pipe from house was cut off at the house! Primary care-giver was out of state at time and my husband who is Trustee of trust arranged to have the septic system working and sibling when nuclear on us saying we were way out of line!
Every flush was piling into the back yard!
And we were out of line for fixing it

Most caregivers are stressed to the max. Your brother is probably no exception. Sometimes we think we are helping when we offer advice but it feels more like interference in an already chaotic life. I suspect you only want to help but it takes the right relationship to offer suggestions to someone who is already treading water.
Often the person who isn't the primary will come in on their white horse and stir things up. Usually it isn't appreciated. What most caretakers want is someone to give them a break. Or money if its needed or respite care or for them to call and talk to mom or dad and brighten their day. Advice, not so much. I assume your brother is POA for your mom? Does he handle medical and financial? Are you concerned he isn't doing a good job with one or the other? Are you concerned that mom isn't safe? Do you know anyone in the area who can pay a visit and let you know how things are going? Is your upset that you have pushed brother to this point or is it over your parents care? Or maybe both? Tell us a bit about the issues that are making you sick and sleepless. Perhaps its time to visit?

You live 800 miles away yet you give advice. I think you could heal relations by asking the care giver WHAT you can do to help. They are likely under alot of stress and your "advice" doesn't help at all. What do they need? Could they use some respite? Those are more helpful.