No. MDE2 and MDE3 would also need to be linked to each other.
I have MDE1 linked to MDE2 and to MDE3.
MDE2 and MDE3 have full Sharing of Plans and Sharing Photopass with MDE1.
In MDE1, I can view all of MDE2’s photos taken in Epcot and Studios last week.
From MDE3, I don’t have access to any photos that are in view on MDE1 because I’m not linked to MDE2 - the originator of the photos.