A Roman Catholic parish church generally has a “pastor” who is the head priest in charge. In some cases the pastor is the only priest, such as if the diocese has a priest shortage and/or the parish is small. If the bishop chooses to assign a second priest to that parish, the second priest will nowadays be called a “parochial vicar”. There can be only one pastor per parish, but there can be multiple parochial vicars, with the one who was appointed first being the most senior.
Some years ago the parochial vicars were called “assistant pastors” or “associate pastors” and some churches might still use this wording, but the current Code of Canon Law uses the term “parochial vicar”, so it’s more correct for churches to follow the Code wording.
In addition to the pastor and the parochial vicar(s), there can be other priests living at a parish rectory who are called “in residence”. In some cases they are retired but still willing and able to help out with some priestly duties; in other cases they are living at the rectory while they primarily serve as priests at a local facility (like a college or a prison).
There can also be “visiting priests” who are usually in the area just temporarily for some reason, such as to get medical care, improve their English language skills, attend school etc and they live at a parish rectory and help out with some priestly duties while there, for example hearing confessions or saying some Masses.