You can claim the 18 year old since she is under 19.
You can claim the 20 year old if she is a full time student no matter how much she makes.
Be sure on their returns they checked the box that says they can be claimed on Someone Else's return. That is very important. If they claimed themselves then you will have to mail your return this year to claim them. And they will have to mail in Amended returns to change to dependent.
On their returns check line/box 6a should not be checked
On a 1040EZ line 5 should be checked for "YOU".
