Most of them probably have a very weak knowledge of every aspect of their faith. One reason for that is the near complete destruction of children's catechesis in the US between about 1960 and 1985. Things are better now, at least somewhat better in many places.
You don't have to have a physically present priest, but the Church always taught that the study of the scripture should be illuminated by the teaching of the Church, because it is the Church that is the container of the deposit of Christian faith, of which the scripture is but one product. In other words, one who reads the scripture and arrives to notions contrary to the sense of the Church, misunderstands what he reads.
30 And Philip running thither, heard [the eunuch] reading the prophet Isaias. And he said: Thinkest thou that thou understandest what thou readest? 31 Who said: And how can I, unless some man shew me? And he desired Philip that he would come up and sit with him. (Acts 8)