You see I thought of that and I realized he must have had ulterior motives if he too is a bender so what I am guessing is that he planned on being the only bender and start the only bending family left in the world so no one could oppose him

You just block them as you go.
One kid is born a bender, bam, instablock. Either that or you keep benders from generating offspring.

But he said to them that their family had the strongest line of bloodbenders. so yeah, I don't think anyone can stop it.

Because when you loose your bending, the "bending chakra", or whatever is blocked and bendig is in the genes.