How twins are born is it to do with strong sperm or something?

It has nothing to do with the sperm. Homozygous or monozygous twins are identical twins. They are called monozygous because they originate from a single fertilized egg which divides in two around day 10th after the conception (twins are same gender, 100%) Heterozygous twins: 2 sperms combine with 2 eggs at the same time, i.e. 2 fertilized eggs (twins could be same or different gender, 50/50)