You have posted your question under other user names, of that I am sure.
The word "pretermitted heir" does not appear in any of the text books I use (and I use the same text books at the HC Judges use). I have had a brief look for you, based on the wording you posted under another user name (if I am wrong forgive me) and frankly, your problem requires too much research (in terms of case law) for me to bash it out on a website. it is just one of those cases that requires a bit of time (and with a whole load of clients on my backside, I cannot do anything other than a quick kill). I suggest you seek the advice of an independent solicitor - preferably an ACTAPS or STEP and suggest they seek the advice of specialist counsel who has the time to sit and consider this.
And for the record, if it is going to the kids, your brother cannot take the money to get him out of debt. Furthermore, if the beneficiaries are under 18 it would require an application to the court under the Variation of Trusts Act 1958 to alter their entitlement. It is not enough for your brother just to agree (I thought I had mentioned this before, but clearly not) to a Deed of Variation.