Complex sentence: He is the eldest of three siblings his younger brother Thirdy is also a basketball player and on UAAP Season 77 he will be joining the Blue Eagles together with his Brother and his younger sister Danni is currently a volleyball player playing for the Miriam College Knollers.
Split into simpler sentences: He is the eldest of three siblings his younger brother Thirdy is also a basketball player and on UAAP Season 77 he will play with his Brother. He will be the part of the Blue Eagles and his younger sister Danni is currently a volleyball player playing for the Miriam College Knollers.