Who are the relatives with whom ties of kinship must be maintained, and does this include all those permanently forbidden (for marriage)?

The preponderant opinion is that it is obligatory to maintain ties of kinship with unmarriageable relatives (mahram), who are: fathers and mothers, brothers and sisters, grandfathers and grandmothers no matter how high they ascend, children and their offspring no matter how low they descend, paternal uncles and aunts, and maternal uncles and aunts.