Mail them in separate envelopes. If you mail them together you risk that the IRS employee who opens the envelope will overlook one or more of them. Separate checks for tax owed with each one.
Penalties:
Subtract any penalty from the amount you owe reported on original 1040.
Don't try to include, but ignore, any new or changed penalty.
IRS will calculate your new penalty on their own and will bill you or refund you.
Are you saying to only send the amount that TT says I owe, then let the IRS do their work and then send me a bill or refund of the remainder? Or are you saying to not send any money at all even if TT says I owe?
You have to pay the tax due on each return. Either include a check or pay online. Send each year in a separate envelope.
Go by the actual 1040X. Line 18 should be your original refund amount and line 22 should be your additional refund. If you paid on your original return it will be on line 16. If there is an amount owed with the amendment, it will be on line 20.
If you have a tax due, do not send the 1040V. Just include a check with the 1040X. Ignore the 1040V. That is for the original return or what the original return would have been if it didn’t need correcting. Don’t pay the amount on the 1040V. Pay the amount on the actual 1040X line 20.
Or You can pay the IRS directly at
Use the IRS Payment page where you can specify the tax year
OR
write "For <tax year> 1040-X" on your check, along with your SSN.
Otherwise your payment might be assigned to the wrong year.
My other advice above comes straight from the IRS Instructions for Form 1040-X.