Considering Tixa (and actually all sectors) is very easy to take over.

You need:

A lot of chemical break lights (attacks at nighttime i prefer) and a merc like Barry to blow up the place. (After i occupy and re-occupy Tixa several times, the only thing standing up are the cell blocks on the west)

I usually attack the first time from the west to sneak in stealth mode to the southern main gate. The snipers keep an eye on the gate while enemies show up and ready to terminate, while another smaller group enters the area on the left of the gate, using a merc with a wire cutter, quickly move them on the roof of the left small building at the gate and throw chemical break lights to be able to terminate the enemies one by one.

Whenever the place is cleared, move mercs on the roof of the L building, including an explosives guy like Barry and move them (stealth) towards the office of the Warden to blow up the outside wall and terminate the Warden and her guards.

After you have taken over Tixa you leave some explosives behind with remote control (RDX and/or C4) on strategic places (north, in the corner of the L, inside de cell, the bedroom, the corridor) make sure before you leave the sector to blow up the fences in the north with grenades. If the enemy reoccupy the place you attack from the north, Barry blows up the place from inside causing a lot of damage and an easy pass through the complex.

--

Considering tanks later in Meduna:

Same story: Nighttime, break lights, and rooftops. You can put a few mercs on rooftops with mortars and shells. Though you have to attack from the north (SAM). Otherwise use smoke grenades to approach the tank(s) without being noticed by them, you then could even use Barry again to put explosives around the tank (once a merc is very close to a tank, the tank cant fire at the merc nor would a nearby tank shoot because a risk of damaging this tank in particular)

You shouldn't make let you intimidate by the brute force of your enemy, also in this game it is for the largest part only bluff. At the end the few left over enemies will try to crawl away from you!