Do paternal uncles and aunts have the right to claim their share of their grandfather's and grandmother's inheritance from properties that were registered in the name of their father's wife (their mother), and which devolved to them after her death, and are they sinful if they consider themselves the sole legitimate heirs to those properties?

If a father registers his properties in his wife's name as a precautionary measure rather than a gift, these properties remain his and are included in his estate upon his death. His parents (your grandfather and grandmother) are each entitled to one-sixth of all properties, in accordance with the verse: "And for his parents, each one of them a sixth of what he left if he had a child." This right transfers to the parents' heirs after their death, meaning your paternal uncles and aunts are entitled to claim their parents' share. You must ensure this right reaches them and ask for their forgiveness for the delay and injustice; for depriving an heir of their share is considered a grave sin and manifest injustice, and an transgression of Allah's boundaries.