No he couldn't file all of them with one form. You have to file each year separately. That's why you got 3 1099G, one for each year's refund. So don't know what you mean by that.
But you might not need to enter the 1099G at all. Did he use Itemized Deductions on schedule A for any year or just take the Standard Deduction?
A State Tax Refund is taxable if you itemized deductions on that prior year's federal return and took a deduction for state income taxes instead of the sale tax. You got a deduction benefit for it so now you have to include it as income. If you took the standard deduction it is not taxable and you don't need to report it.
