When three of Alluka’s requests are fulfilled, she’ll grant one wish. There probably isn’t any limit to the wishes she can grant. My guess is that she can grant any wish.But the bigger the wish she grants… The bigger the next three requests will be. In other words, an equivalent exchange.And the sacrifice isn’t made by the one whose wish was granted. It’s the next person who fulfills the requests.
If someone denies four of Alluka’s requests in a row, that person and their most loved one, meaning a minimum of two persons, will die. The bigger the wish, the more people will die when the requests aren’t fulfilled.