In my article, I stated:
It was not Saul’s desire to speak with Samuel that was his sin but the forbidden means by which he did so. It would have been fine for Saul to have prayed to Samuel, asking for his intercession—in much the same way that Catholics pray to saints and ask their intercession but do not seek to bring them back from the dead. Instead Saul had a medium “conjure” Samuel.
The sin of necromancy is not merely “speaking to the dead,” although it is sometimes defined that way in a colloquial sense. Necromancy is the attempt, through occult practices, to contact and communicate with a deceased person in a way that brings that person back from the dead. Speaking to a saint or to a deceased relative or friend through prayer is not necromancy, because Christian prayer relies upon Jesus, as intercessor between God and man, to facilitate the communion. In fact, one reason why it is a sin to use a medium as a go-between to the dead is that it is a denial of Christ as the one true Mediator (1 Tim. 2:5).
As for whether you can ask deceased relatives to intercede for you, we may hope that they are in a position to do so, whether they are in heaven or in purgatory. Whether or not the holy souls in purgatory can intercede for us is an open question, but there is no harm in asking for their intercession and trusting God to answer our prayers in whatever manner he wills. More importantly, though, our primary obligation to our deceased relatives, and to all the holy souls, is to pray for them.