The title suggests a shift from the first installment. If the original was about a specific relationship, the sequel—emphasized by "muragaru" (swarming)—indicates an escalation.
Kaasan no Otoko 2: Saiai no Haha ni Muragaru Otoko-tachi – The Return of a Taboo Masterpiece kaasan no otoko 2 saiai no haha ni muragaru o new
However, if you’d like, I can write a explaining: The title suggests a shift from the first installment