Waht are the chances more of my children will have tibial hemimelia?

It depends. There are two types of tibial hemimelia. The bilateral "syndrome" affects both legs and is believed to be autosomal dominant, so there would be a 50:50 chance that another child will be born with it. The unilateral tibial hemimelia (1 leg affected) is thought to be autosomal recessive and a 25% chance (1 in 4) of a child being born with it, and a 50% chance the child will be a carrier.