Complex sentence: He was born in Switzerland to a family originating in Savoy and had eight siblings, including Jacques' two elder brothers Augustine (born 1723) and Jacques (born 1725), who both served in the army of the King of Sardinia then the Dutch Republic.
Split into simpler sentences: He was born in Switzerland to a family originating in Savoy and had eight siblings, including two elder brothers Augustine (born 1723) and Jacques (born 1725). They both served in the army of the King of Sardinia, who then ruled the Dutch Republic.