Child tax credit

You are not eligible for an advance child tax credit payment (or child tax credit) for your 22 year old college student.  You would most likely be eligible for the Other Dependent Credit for him/her in the amount of $500.  The 16 year old would qualify for you to receive the child tax credit of up to $3,000 on your 2021 tax return.  This would mean your advance child tax credit payments would be $250 per month from July through December ($3,000 / 2 = 1,500 / 6 = $250.  There could be numerous reasons why you have not been receiving the advance child tax credit payments.  If your address and/or banking information has changed since you filed your 2020 tax return, your advance child tax credit payments might not reach you.  Another reason you may not have received them is that you may have accidentally claimed the Other Dependent Credit on your 2020 tax return for the 16 year old.  You might want to take another look at your 2020 tax return to see if you claimed the Child Tax Credit or the Other Dependent Credit.  If you claimed the Other Dependent Credit you can amend the return to claim the Child Tax Credit.  You will see Child Tax Credit on line 19 on page 2 of Form 1040.  Then there may also be an amount for Additional Child Tax Credit on line 28 on page 2 of Form 1040.
Either way, if you are eligible for the child tax credit for the 16 year old, it will be on your 2021 tax return.  If you didn't receive any of the advance payments, then you will claim your allowable amount up to the full $3,000 on your 2021 tax return.  (If you had received any of the advance payments,, they would be subtracted from the $3,000).