I dont under stand what you mean by Engineers will build the????
CI and GOI would constantly be at each other's throats over the raid timer. This would be made worse do to their close proximity to each other.
CI and E11 already had this problem with the old old very old Charlie 5 (the one before the thumper) and that caused a lot of bad feelings between the two branches, having these to branches next door to each other and having them fight over raid time and over who controls the town would be toxic shit.
(E11 would probably have a good laugh from on top of the Mountain though)
Another problem would be the foundation research it's bad enough having CI raiding and causing defcon 2s all the time and stealing the few SCPs that are online. Doubling this factor would do greater harm to the branch.
The only way this could work at all would be to turn CI into the GOI and removing CI
Which could be fun.