Vinchen should just report to his father that the eldest brother is unqualified to be heir. He was barely able to beat someone at least 15 years younger so clearly he lacks talent, he was easily angered so he lacks political foresight, not to mention his backing is of traitors and he hasn't helped the growth of the family.
Of course he will instead be a minor villain causing problems until Vinchen becomes strong enough to kill him along with the elders.