I'm wondering it is possible to send infopath form to all, but only few to email notfication.   When I try to use Notification event designer, it doesn't allow to
modify email "To" field that would been simple solution for this.

For Infopath client approvers event, the option to plan per destination and all at once, it runs as a parallel destination. 

With email notification turns on, they will all get email notification.  Is it possible to send only pre-defined approvers only? 

I can use custom email notification, but I can't create worklist item url in email body because I don't know what is activity destination id is for that specific approver (multiple recipients (ids), but only selected pre-defined email notifiers).   In other world, Infopath form is sent to every one in that group, but email notification goes out to few in the group with worklist item url in the email body.   Some how if I know how k2 creates unique activity destination id, I think it will solve this issue.   Thanks.