My uncle just died. They own the home mortgage free. He is 24
The tax question is far too complex to answer in this format. Yes, it would most likely avoid probate in regards to the house. However, probate may be necessary for other reasons, and adding someone to the house is not a great idea. If grandson ever ends up running into financial trouble or even gets a divorce, then that house is counted as his property and would be subject to that court process or could be attached by his creditors.
What taxes are you trying to avoid? Gifting does not avoid taxes, and can actually accelerate transfer taxes and possibly increase property assessments. Transferring to joint tenancy would achieve the result of avoiding probate, but its really not the greatest estate planning tool because circumstances could change for grandma or grandson could develop bad habits that grandma doesnt like or could turn on grandma and force the sale of the property.
Grandma should really meet with an estate planning attorney to go over her options.
I agree with my colleagues. The answer, in large part, depends on how this is done. Your aunt should visit with an estate planning attorney. She needs to set this up properly, in order to avoid all kinds of possible problems, down the road. There are ways to set this up that will likely achieve your aunt's goals. She should not attempt to do this on her own. There is also additional estate planning your aunt will need, including durable power of attorney forms for medical and financial matters. These avoid the need for probate during lifetime, in the event your aunt becomes incapacitated.