It is not a problem from an ethical standpoint to have us do a session on behalf of your brother that is not asked for and he will be unaware of. The only sticking point is that if you sponsor a session on his behalf, that he not be told subsequently that you have done this. People will feel uneasy and may well feel violated to have someone seemingly tinkering with their mind, even the divine; it just does not sit right with people and may well cause a backlash against you and against the divine as well. So there are karmic responsibilities in being a sponsor for a third party, to be discrete and maintain privacy if you choose to go around him, and this we understand is advisable in his case because of his nature.
As to prioritizing between you and him, that is your business to decide. We cannot take the lead here and elevate him above you nor you above him, as you are both worthy souls and we have to be neutral with respect to treating all fairly, meaning equally, whether or not they differ in need and worthiness with respect to how they have conducted themselves in the current life or even through many prior lives. This is a burden you do not share as you are not living from the divine vantage point, so you can make personal decisions that favor the self, for example, and that will not be counted against you because, after all, you are the guardian of your soul and no one will look out for you if you do not. There is no virtue in sacrificing yourself to help another. This is something you can choose to do, but we will not fault you for not doing so. So you must simply decide what your desires are here and either choice you make will be honored and respected because, after all, both choices have merit and need not be seen as an either/or. You may even think of the current situation you face as priming the pump to see to your own growth and healing because you are in the best position to be a wage earner and provide funds for further healing for you as well as family members. So that is not a divine decree but merely the fact that you will not make a misstep here—the choice is yours.