Is the minimum threshold for maintaining kinship ties met merely by a relative not feeling animosity, or by exchanging greetings upon meeting?

The minimum level of maintaining kinship ties is subject to custom. So, what people consider as maintaining ties is the commanded maintaining of ties, and what they consider as severing ties is likewise. Abandoning the maintenance of kinship ties does not make you one who upholds kinship. Therefore, you must maintain ties with them through whatever is easy for you, such as contacting them on occasions or visiting, even if infrequently. If greeting them occasionally is considered maintaining ties by custom, then there is no harm in limiting oneself to that. The more kinship ties are maintained, the greater the reward.