I have given myself a construction contract for a Redoran stronghold,
I already completed the Hlaalu quests, and have a Hlaalu stronghold.
I force joined Redoran, and have made it to the stronghold quest, but
there is already a stronghold there (at Bal Isra, because I completed
the Hlaalu quests). How do I build the stronghold? Do I need to
remove the existing buildings? or is there a console cheat?

to get the construction contract, I consoled.....
player-> additem "bk_stronghold_c_hlaalu" 1
this is because there is only 'Hlaalu' listed in the files, and it was
accepted by the nice NPC who is building the Redoran stronghold,
I would like to own all 3 strongholds, because I am going to
complete everything there is to do in this game. because i am special
and deserve to own all of Tamriel.

Thank You for your attention to this matter,

Booger the Hack