Thanks for the additional information.
I'm afraid that I do not have good news for you. While there may have been an agreement between the Beneficiary of the pension plan and your mother, or even between the beneficiary and you and your other sibling, those promises were bare promises, not supported by consideration and did not create a legally enforceable contractual agreement.
Neither does the fact that he may have in the past actually made payments that corresponded to the promises made mean that he has somehow unilaterally created a contract.
The deceased did nothing more than name a beneficiary of her pension, and under law, the pension assignment was a contract and the only contract in this regard.
There is no law being broken by your brother failing to continue to divide the payments as you say was promised. He has broken a promise to each of you and perhaps to your mother as well, but that does not give you any legal recourse.
Were you to tell me that there was a written contract between your mother and the beneficiary indicating that she would name him as beneficiary so long as he would agree to the division of the money, then I would say that as a third party beneficiary of that written contract you have grounds to sue to enforce that contract. However, absent such a contract, you have no legal basis to sue. I am sorry.
I understand that you may be disappointed by the Answer you received, as it was not particularly favorable to your situation. Had I been able to provide an Answer which might have given you a successful legal outcome, it would have been my pleasure to do so.
If you have additional questions, you may of course reply back to me and I will be happy to continue to assist you further until your questions have been answered to your satisfaction.
Would you please take a moment to positively rate my service to you based on the understanding of the law I provided by clicking on the rating stars---three stars or more. It is that easy. That is the way I am compensated for having helped you.
Thank you in advance. I wish you the best in your future,