I just took them in for their final kitten vaccinations (they're about 16 weeks old), and Sergey weighs 4lb 11oz, and his sister weighs 3lb 13oz. She was the most petite of their litter, and he was definitely the biggest
Figures may change as they grow older. My little Yon has overtaken all her brothers in the weight department and she was the tiniest one of the litter.