Before doing that, follow the advice and explanation of Mikrotik support’s IPsec expert @emils in this almost identical thread.
And I have to apologize for misleading you - in my setups it is actually always the initiator which has two WANs, so the intuitive (and wrong) understanding of the purpose of the send-initial-contact=no as something just preventing the peer from actively initiating the establishment of the IKEv2 SA doesn’t prevent the setup from working because in my cases, I do have this setting on responder side (activated using passive=yes) which is also the side where a common IP address is used for both IPsec “sessions”.