What is the ruling on going to the Jumu'ah prayer early despite parental opposition, given that the only way to go is with a brother who delays the prayer?

You should continue advising your brother on the importance of arriving early for Friday prayer. Obedience to parents is obligatory in what is good and permissible, but it is not permissible if it involves neglecting an obligation or committing a forbidden act. Allah has made it obligatory to hasten to the Friday prayer upon the call, which is the adhan after the Imam ascends the minbar. Therefore, whoever hears the call and is obligated to attend Friday prayer must hasten to attend the sermon and the prayer. If one's home is far, it is obligatory for them to hasten before the call to catch the sermon and the prayer. If going with your brother causes you to miss this obligation, then you must go by yourself, while explaining this legal ruling to your family.