Is the decision not to visit siblings who mistreat and do not reciprocate visits considered a severing of kin ties, and does it entail sin, especially in light of the desire to raise children to uphold kin ties?

Allah has commanded the joining of kinship (silat al-rahim) and prohibited its severance. A severer of kinship will not enter Paradise. Severing kinship causes Allah to cut off the one who maintains ties. Allah has commanded us to maintain kinship even with those who sever ties with us. Not asking about siblings is a form of severance, but it does not permit you to cut them off. Visiting a sister weekly might be burdensome. It is advised to repent from estrangement and to persevere in maintaining kinship ties, seeking Allah's pleasure, for in it there is blessing in sustenance and life.