We are able to answer tax questions here. We can say that your niece does not have to enter the gift on her tax return because gifts received are not taxable. The person who gave the gift does not pay tax on the gift if it is below the lifetime amount of more than $11 million. If the gift was under $15K per grandparent in the tax year to any one individual then they do not have to complete a form 709 gift form.
As for your concerns about the inheritance----that is not a tax question. That is a legal question and also gets into the area of the discretion the grandparents have to do whatever they choose to do with their money. They can assign amounts as they choose to when they complete their last will and testaments.
Money that you receive as a gift is not taxable income to you, and you do not need to report it on your income tax return. Money that you gave as a gift to someone else is not deductible for your taxes.
Turbo Tax does not support the gift tax form 709, but here is a link:
https://www.irs.gov/pub/irs-pdf/f709.pdf
https://turbotax.intuit.com/tax-tips/estates/the-gift-tax-made-simple/L5tGWVC8N
https://www.forbes.com/sites/ashleaebeling/2017/10/19/irs-announces-2018-estate-and-gift-tax-limits-...
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
