Barbara and thanks Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
I am afraid that the 3 of you have no claim against his Estate.
Any monies of your Father's passed to your Mother on his death. As such, she was then free to do with that money as she so wished. Likewise, any monies your stepfather has gained from your Mother was his.
Sadly, your Mother should have made a Will leaving the 3 of you whatever monies she wanted to. As this did not happen, the monies held by stepfather do now legally pass in accordance with his Will.
I am sorry this is not the answer you were looking for, but it sets out the legal position.
Can I be of any more assistance to you?
1. As with a Will, a codicil is a private document until Probate is issued. Therefore, there is/was no need to be registered with a third party, and it would normally be found located next to the Will.
If your brother, who was adopted,has been excluded from the Will, he would have to show that he has been financially dependent on your stepfather to enable him to have grounds to make a claim against his Estate.
I am sorry I can't give you any magical answer.