Unless the deceased relative is a ghost then it’s not likely you’ll be able to communicate with him without major professional paranormal intervention. It’s the same reason why all dead relatives don’t simply come back and visit us. Clearly in the great beyond, freed of their physical body, they’d have the power to return in at least a ghostly format. Who wouldn’t want to come back, and reassure their family that everything was okay. They should miss us right? The fact is that the afterlife exists beyond time as we know it so everyone who will die in this Universe to the very end of the future is already in the Heavenly realms. That includes yourself. You’re already there with your relatives so they have no reason to return, or heed your need to speak with them. From their perspective your life ended a long time ago, and they’re speaking with you in the afterlife right now. You just need to wait your life out, and you’ll be with them once again.
There’s also the likely possibility that our soul is the melding of our near infinite parallel lives in the near infinite parallel Universes that scientists think exist. If that’s the case then we’re totally different people in the afterlife, and this one little life you’re in wouldn’t even be on the radar of your relatives.