Is greeting an abusive brother and visiting him at a relative's house instead of his own, as well as greeting a harmful female cousin only on occasions, considered sufficient to maintain kinship ties? And is a female cousin considered kin whose ties must be maintained?

First: What your brother did by harassing is a reprehensible act and goes against human nature. You were right in not visiting him, not isolating yourself with him, and preventing your daughter from being alone with him. A simple greeting when you meet him is sufficient as a way of maintaining kinship ties for people like him.

Second: Your cousin is among the kin whom one should maintain ties with and treat kindly. Scholars have differed on the exact definition of the kinship that must be maintained. Some have restricted it to mahram (definition) relatives (such as fathers, mothers, brothers, sisters, paternal uncles, and paternal aunts), while others have obligated the maintenance of ties with all relatives (making no distinction between mahram and non-mahram, like a paternal cousin). Whether your paternal cousin is among the relatives whose ties must be maintained or whose ties are recommended to be maintained, there is no blame upon you if associating with her causes you harm, and you limit yourself to greeting her at family gatherings. You will not be considered a severer of kinship ties by doing so.