3 year old son against twins!?

I am expecting twins and me and my husband told our oldest kid first he is 9 about the twins, then told our 5 year old daughter. They where both excited.But our 3 year old Ethan is used to being the baby of the family and now there will be 2 new babies. He told me that he didn't want the twins and he wants them to go away, so he can sit on mommy's lap again.How do I get a 3 year old to be okay with his new twin baby siblings.