Egypt ability (to build a building for 0 hammer as a City action) cannot be combined with Engineering.
I think it's obvious that you cannot build 2 free buildings as a City action with Engineering. But can you build one of the 2 buildings for 0 hammer and use the normal production value of the City to build another building (or even something else) ?
I don't think it was clearly mentionned in the rule. I'm even wondering if the rule was only made to forbid the 2 free buildings in a single action.