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In the US - gift - is not taxable income for the recipient and you do not need to report it on the tax return.
There is no any amount limit.It does't matter how the gift is transferred - as long as that is a gift - there is NO income tax liability.
Please see for reference IRS publication 525 -
Gifts and inheritances. In most cases, property you receive as a gift, bequest, or inheritance is not included in your income. However, if property you receive this way later produces income such as interest, dividends, or rents, that income is taxable to you..
Another issue with gift tax...
Regarding your situation - if the donor (gifter) is an US person - the gift is reported on the gift tax return. The gift below $14,000 is not taxable gift but when the gift is above that threshold - it is reported on the gift tax return - form 709.Regardless - there will NOT be any gift tax liability as long as the lifetime limit is reached - that limit is $5,430,000 for 2015.
If the donor is NOT an US person - and is a nonresident alien - the donor is not under US jurisdiction and does not need to report the gift.
However if you receive above $100,000 from a nonresident alien and if the total amount is above $100,000 - such gift is reported by the recipient on form 3520 -
So far - based on your information - donors are your grandparents who are nonresident aliens and the total gift amount is below $100k - so there will not be any tax liability and NO reporting requirements.