OP I have a relative who has been sectioned, and I just wanted to offer you some support and a hand hold, if you need it.
Although the mental health problem of my relative was very different to the one your DB has, I know that the section in itself is unpleasant, and families tend to feel a stigma, as if they haven't done enough so the state has to step in.
Of course, that isn't true, and we should feel no shame at all, but it's not always easy!
I think you should support your parent rather than your DB at the moment. In particular, try to be united in not giving money for drugs, drink etc. Your brother is at least 'safe' in hospital, and you all need this time to regroup and recover a bit.
I don't think you should expose your children to this level of illness, especially if they have expressed worry / fear already. My children were much older, but still found all the odd experiences they had in my relative's company rather scary!
When the time comes for your brother to be discharged, be very firm with SS about what you are and are not prepared to do! Better to promise only a little, rather than too much and it all go wrong later.
I hope your DB gets good treatment and you find a way through this as a family.