The broadest definition of a "saint" in the Catholic Church is someone who has died and is now in Heaven. The word saint is derived from the Latin word sanctus, meaning “holy,” and refers to all the faithful who strive after a life of holiness.
In fact, the only way we can enter into Heaven is if we become a saint.
For Catholics, this can be accomplished in a variety of ways, but hinges on those final moments of our life on earth. We can either embrace the love of God and be drawn into his light, or we can reject his love and choose an eternity of loneliness and despair.
We may accept the love of God during those last moments of our life, but still need "purification" after death.
This purification is accomplished in what Catholics call purgatory, a final state of preparation before entering the gates of Heaven.
If we weren't perfect saints during our life on earth, but still chose to follow God during our final moments, we can be purified in what C.S. Lewis called the, "washroom of Heaven."
This is good news for all of us, but also for our deceased relatives. We don't know exactly what went through our relatives' minds during those final seconds of life, and whether or not they expressed to God their heartfelt repentance for all their sins.
However, we can hope and pray for our deceased relatives that they reached the purifying "fire" of purgatory and are being prepared to become a saint in Heaven.
They might even be in Heaven already, looking lovingly down upon us, urging us on to make the right choices so that we can join them again in eternal life.