I have 2 kids to an idiot but he keeps threatening me saying he's going to get them taken away from me cost he wants them all to his self how can I stop this happening

First, you need to stop calling him an idiot. Even if he IS an idiot--YOU slept with him. TWICE.

The next thing you do is get custody established through the courts. I suggest a lawyer. IF you are not doing drugs, have a stable income, have a stable home life and are treating the children well, he has no just cause to take the children away.