Which of the following matters has priority for a believer: performing 'Umrah, or buying graves, or performing the 'Aqiqah for children?

It is better for you to perform Umrah (definition). If you have not performed Umrah, then it is obligatory upon you if you are able. If you have already performed Umrah, then Umrah is better than Aqiqah (definition) and better than purchasing a burial plot, due to its great virtue. Aqiqah is a confirmed Sunnah (definition), and it is better than purchasing a burial plot for yourself or your family. Purchasing a burial plot is permissible, and there is no indication in the texts encouraging it, but there is no harm in purchasing it if one has willed to be buried in it. Uthman and A'ishah did so.