Hi White Pumpkin,
You may find this article on Disclosure and Confrontation
If you think your mother will be receptive to the information, I would tell her what your brother did to you, and then tell her of your concerns for your nieces and nephews.
Since you said your brother is not honest with you along with the description of him being a con-man, I do not know that speaking to him, at least privately, will accomplish the goals you seek.
Before you confront your brother you may want to discuss this with your therapist, if you have one. If your mother is supportive, you may want to include her in your planned
confrontation with your brother.
Please carefully read the section on Confronting the perpetrator.
You want to make sure your needs are met and that this does not turn into a situation in which your brother manipulates and emotionally abuses you.
Just my $0.02.