Inheritance enquary

Iv been trying to get hold of transnet ****rnets finance department. My brothers late dad always mentioned he had enlisted him to get something when he passes. Our mom passed away in November. And myself bieng the older person his altermatly my responsabilty. His is on the autism spectrum therefor even though he is 19 he needs assistance with such. Where to i go about embarking on this jurney. He is a child outside of mariage and was never included by the wìfe regardless of knowing about him. Please help.