I mailed my returns with 2 checks to the IRS on 4/12 but the money has not been withdrawn from my bank account. How can i be sure that payment was received on time?

If the envelopes were postmarked by the filing deadline of 4-15 (and you say you mailed it on 4-12) it is "on time" even if it takes the IRS/state a few extra days to cash the checks.   Just watch your bank account for the payments to be posted.

I paid the IRS and state on 4/3.   IRS cashed on 4/12.  My estimated payment in Dec took 9 days  too.