During the battle, policemans go randomly here and there with a psychotic tendency to group near your mercs. You may use this behavior to your advantage (at night for sure) firing to enemy with a coop just in LOS ("woops, sorry good policeman i never wanted to hit you! :blah:") or let the enemy fire at you, sometimes it's possible, it's more dangerous for sure but take in mind that if you "accidentaly" hit them, killing them, after a while (2-3 pheraphs 4 coops killed) they becomes however hostile and generally in the worst moment... So doing this you may erase few of them, but sometimes "few" is enough, morale is easily recovered

A classic to solve different problem in JA2. With a TNT :
1) go to the back of the cellars (from outside)
2) place the tnt about 1 or 2 tiles away from the building west corner (near miranda cell)
3) arm it (as for the time 3 or 4 turns) run away with all mercs, staying away from any coop visual range. May be that this is not necessary, but i found that sometimes coops become hostile even if nobody is hit by the explosion but they may see you.
4) obviously save first, take the point 2 only as a generic hint (i can't remember the exact point in wich TNT mut be planted) and try

5) If by chances Miranda become hostile, exit map without doing nothing and re-enter (not totally sure if this work)