Do I need a real estate attorney to begin this process, and do the decendants of her siblings have rights to any of the profits?

You need a real estate attorney who is also familar with probate/estate issues. If your aunt's mother died intestate, there are state laws that will determine who should have obtained ownership in the property. You didn't state how long she's been living in the property or if her siblings have claimed an ownership interest. In any event, she will be entitled to a credit for improvements in the house.

However, the first thing is for her to interview several real estate/probate attorneys and select the attorney who best fits her needs (experience, comfort level, and costs). Although I am an estate planning attorney, this is not the type of case I would handle.

The answer to this question will most likely require you to retain a probate attorney or a real estate attorney with probate experience. You must determine if your great aunt's mother died intestate, this transfer will be governed by intestate succession law (i.e. without a will). A probate or estate lawyer can advise you. If your aunt wants to sell the property, the rights of the nieces and nephews to the property will be determined based on her mother's death (and the succession from there), NOT based on transfer via your great aunt's will.