Private revelations from saints in Heaven are possible, and the Church has approved many of them.
After someone dies, it can seem like there is a wide chasm between our world and theirs. Yet, the spiritual world is much closer than we think, and on rare occasions certain individuals have been given a glimpse of it.Death is the separation of body and spirit, and for those who go to Heaven, their souls remain in complete and total union with God. This union has an infinite number of benefits, and one of those is the ability to move about freely, with the possibility of visiting people on earth.
Strictly speaking we know very little about this phenomenon. What we do know is that Jesus Christ visited his apostles after his death and resurrection, showing that this type of interaction between deceased and living is possible.
The Catholic Church does recognize that besides Jesus, others in union with him in Heaven can make occasional visits as well. This includes angels and saints, most notably the Blessed Virgin Mary.
However, the Church does not easily approve of these private revelations, as they could be demonic deceptions, or part of a person’s own imagination. A Vatican document that was drafted in 1978 describes the steps needed to confirm a private revelation. After those steps are completed, on certain occasions, the Holy See may decide that a particular apparition or message is universal in character and can benefit the entire Church, labeling it “worthy of belief.”
It is possible that individual persons may witness an apparition of a saint (meaning, anyone in Heaven), but those instances are difficult to discern. This is why any instance should be brought to a trusted spiritual advisor, who can help see if it was authentic, or only an illusion. The Vatican document mentioned above can also help in the discernment.
The basic answer is “yes,” saints can visit people on earth, though this happens on rare occasions and for a specific purpose in God’s divine plan.