Complex sentence: The Buriat make up only 25% of their own Republic, and the Sakha and Altai each are only one-third, and the Chukchi, Evenk, Khanti, Mansi, and Nenets are outnumbered by non-natives by 90% of the population.
Split into simpler sentences: The Buriat make up only 25% of their own Republic. The Sakha and Altai each are only one-third of the population in their traditional territories, and the Chukchi, Evenk, Khanti, Mansi, and Nenets are also outnumbered by the non-natives who make up 90% of the population.