I think of it this way. In the same way you could ask a friend of yours here, on earth, to pray for you, you can likewise, ask someone who has died to pray for you. This is because we believe that they are alive.
I generally don’t ask those who have died to pray for me, though. I do exactly the reverse. Unless the person is canonized a saint, I pray for
them! Well, have you ever read about the difficulty we have in getting into heaven? The Bible says that even the just man will barely get in! The only reason it’s possible at all is due to God’s grace.
In order to get to heaven, we have to be PERFECT, NO sin! How many people do you know who you think are sinless?! Do we know any?
I’m not saying the person in question isn’t saved. I just think most people who go to heaven make a stop in purgatory, first, is all. So, if doubt, I would pray for that person. As to asking for intercession on my part, I prefer to ask Jesus, the Blessed Virgin Mary and the other canonized saints for help in that area.
romancatholicism.org/jansenism/fathers-fewness.htm