If you have taken a loan from a bank wherein you have the funding account, I am very sure that the Bank would have put standing order for each and every EMI on the due date to be debited to your sb or funding account and to be credited to the loan. However, if you intention is to have one day where all three debits take place, you can approach the bank and ask them to change the EMI to one fixed date. I am sure the bank will oblige.
I don’t think currently there is anyway of clubbing all EMI in single transaction.
Even if you have all 3 loans from same bank, at bank end there will be separate loan account number for each loan and 3 separate transaction would be required.
Also, duration of each loan would be different too, so I doubt bank would like to club all transactions in one.
So you might be able to ask bank to do all transaction on same day, but it will still appear as 3 separate transaction.
But just curious, what exactly is the advantage you see of doing this? I assume all EMI would be auto debited and there is not manual effort involved on your part, so what is the benefit of this?