You will need to use :merge with and :unique item
So a first search will look for Sender = Current user and Receive = Curren’s user observings user :merge with do a search for… Sender = Current user’s observing user’s and receiver = current user : unique elements
However, you can consider to have a field that have both information (involved, list of user) and you search for the list to contain Current user AND Current user’s observing user. It will reduce the number of search
I used the first option and it worked great! Thank you so much!
use :sorted by
And select the field you wan’t to use to sort the whole list. This need to be the last step
Thanks Jici
Your solution helps me as well 

