Hello.

In order to achieve the goal, you will need to take a few steps. There should be a written agreement in place between the two siblings specifying that this particular income is to be received for each of them equally, and that the division shall continue for as long as the income is being paid and that the payments shall be made to the estate of either upon their death. It is important this be in writing (as it sounds like just an informal agreement now to divide the money), as this is necessary to ensure the agreement is respected when it is no longer just the two of them involved. Second, each would have to establish terms within their respective Wills in the form of trusts that the ongoing income is to be divided among their heirs of each. As you are talking about a trust taking effect on their deaths, this must be set up within their Wills.

I would suggest that you consult with a lawyer that is familiar with drawing up Wills to do this work. This is not mandatory to make such an agreement and Wills valid, but I very much believe you can avoid much possible confusion or problems or unwanted tax effects (or even acrimony among family members) by paying a lawyer now. If a lawyer is needed only in the future if such an agreement or Wills are not done properly, there is no doubt that will be much more expensive.