Is refraining from communicating with one's maternal aunt and her children considered unlawful (haram) if communicating with her causes many problems?

It is obligatory to maintain ties with the Mahram (unmarriageable kin) relatives. As for non-Mahram relatives, it is recommended but not obligatory. Maintaining ties with the maternal aunt (Khala) is obligatory because she is in the position of a mother. However, maintaining ties with her children is not obligatory. It is also obligatory to maintain ties with a relative who causes harm, in a manner that does not result in further harm.