Borrow money from relatives, do IRS need me to fill tax on it?

No.
Think about it. Credit cards are borrowed money that must be repayed, but you dont have to reported them to the IRS.

No, the IRS doesn't care.

it is not reportable income
you might have some requirements to reporting foreign money brought into the US

in case you under no circumstances filed 2008, i can't see you having filed any style of extension by 4/15/2009 while it became due. in case you particularly had an extension, it could have held the window of opp open till 8/15/2012. notice, if the IRS believed you owed funds for 2008, submitting despite in case you could't get a reimbursement is worth it--a minimum of you could convince the IRS you do no longer owe.

Actually the IRS does care. Your relatives owe 30% of the interest income as tax and you, as the payer, are responsible for withholding the money and sending it to the IRS. You report the interest paid on form 1042-S each year.

See IRS pub 550 to determine the minimum interest rate they have to charge and then see IRS pub 515 to see how to send the withholding in.

No. Money that you borrow is not income. You are not required to report it. You are not even allowed to report. If you do attempt to file tax on it and the IRS checks, you will be in a lot of trouble for trying to file taxes on something that was not income.

However, if they do not make you pay back the loan, then you must report, and file tax on, the amount that they "forgive" or "cancel", when that happens, not now.