There are tons of ways to handle the towers. Most groups will portal the squad up & back down, some like to have a small, dedicated tower team instead. If you feel fancy, you can Solo Capture.

Bring Greatsword + Focus offhand. Start on your focus set. Focus pull the group into the middle, swap to greatsword, use GS 5 to push the grouped mobs towards the little spaces on the turret. I like to bring the daze mantra to stun them before they can run back in to allow myself extra time to get the capture.

The capture ring doesn't extend fully to the edges of the turret and is a little off-center. Use that to your advantage to group up + push the White Mantle out. All you have to do is outnumber them inside the capture ring.

If there's a Cultist, pray they don't spawn a minion - your focus can only pull 5 targets, there's 5 White Mantle on the tower. If a minion is spawned, there's a chance you pull it instead of one of the White Mantle. 😃 I like to try to stealth as soon as I land to hopefully prevent them from instantly aggroing + spawning minion. Sometimes it works. Sometimes it doesn't. I got really lucky here and managed to focus pull the 5 White Mantle.

If this doesn't work, I usually just portal the group up for that specific tower and try again on the next.