How do you get one stubborn brother to tell his younger siblings about their father who has a medical issue?

If he has tried and they don't want to listen then its on them. Tell the SIL to tell her husband because your husband tried to and her DH would not listen.

When ur asked what is wrong with Dad, tell them that ur DH tried to tell them and they didn't seem interested then send them to your husband.

Do not pressure your husband. Are you caring for FIL in ur home?

It is not your husband's job to tell the others. If dad wants them to know, dad should do the telling.

In fact, if your hubs is the POA, it is a violation of the POA to tell anyone.

Job of POA is to keep information private.

Call a family meeting so your DH can sit the brothers down & have a heart-to-heart talk about dad's health issues, which is dementia/ALZ since your profile indicates as much, and since you've put your question under that category.

Does your DH have dad's medical and financial POA? Hopefully so, b/c once an official diagnosis has been made, POA can be quite difficult or impossible to obtain.

What I have found from reading this forum for years is that A LOT of men are in denial about dementia for their parent(s). They just have a very hard time believing their invincible parent(s) could possibly be suffering from the dreaded d-e-m-e-n-t-i-a or Alzheimer's and refuse to wrap their minds around it. Until it becomes so obvious that dad is wandering down the street naked or something equally in-your-face. A family meeting to discuss the reality of what's happening and down-the-road care and management of dad is what's needed and required moving forward. Whether the 'boys' like it or not is irrelevant: the truth must be spoken out loud.

Best of luck!

It's a guess - are you talking about an inherited condition like Huntington's or something?

Based on the little you've described so far, your wisest course of action is to zip it. But what potential consequences do you think might arise from their ignorance?

I doubt that they don’t want to accept that their father’s getting older. It’s to their advantage not to listen, so they don’t need to do anything to help.