"A neighbor is saying he had his property surveyed and says my aunts buildings and fence are on his property even though they have lived there for 30 yrs and paid taxes the whole time. This is in Iowa do they have to cede the land back to him? Thanks"
Before your aunt does anything, she'd be wise to fund her own survey.
Once she knows for sure if the neighbor is correct, discussions can begin as to what the best solution to the matter should be.
If it is true, the neighbor may be able to make a claim to the property under the theory of adverse possession.
He may already know that, but it is always better to say as little as possible, which in my view is NOTHING.
If the amount of land is smal, there are other options that might need to be considered.
Bottom line, engage a survey (by a state certified surveyor) and discuss the matter with a couple of local real estate attorneys.
This could be very expensive for your aunt.
So she should say nothing about the matter except she will need a month for her attorney to investigate the matter.
Whatever is done, remain calm, be polite, and say nothing more.