I understand. as far as your bro goes, you know what, you should have a clean conscience. do what you think is right even if there is no reciprocity in his approach, and well dont do it to your detriment, but be assured in knowing that you are doing what is right. Dont let your brothers misgivings, complexes, and what nots impact what you can accomplish. There can be a hodgepodge of things there, you being in late 20s probably puts in in 30’s, and he may be lashing out against you because previous jealousy and possible current lack of satisfaction ion what he is doing is making you a scapegoat, people are strange that way, and this is what i noticed with a pal of mine. In his case it was actually more nefarious, brother essentially wanted to tale over the family house and created a big mess and major fight, estranged younger brother from parents and all, got the house..dunno maybe I am reading too much into similarities here.
every person has different motivations for success, thirst for knowledge, challenging their limits, being the best, proving everyone including themselves wrong, proving themselves right, a passion for a field..list goes on.