If I was playing the giants and they realised what happened, giant one would simply shake his friend out of the spell. Then giant two would attack
Perhaps now have FG1 instead shake FG2 awake, and then FG2 will attack on the same initiative count?
Sounds like a fair tactic to employ, particularly after missing the wizard twice this round.
Giant 1 (with the cold weapon) went first in the initiative order, then giant 2. Giant 1 failed the save, giant 2 succeeded. Even though they go on the same initiative count it wouldn't be fair to let them change their order whenever they want. For example, if my fighter and wizard both had an initiative of 15 (and both have the same Dex) I wouldn't let the fighter go first one round then let the wizard go first the second round. If the PCs can't do it, the enemies can't do it either.
Plus it was already unlucky that the giant made his save at all! No need to make it even worse by allowing them to switch initiatives.
Giant 2 had every reason to believe he would be able to flatten the robe wearing human. The wizard looks to have an AC of 12, +2 for the cover from the fighter is 14. The giant can't see the Mage Armor (+3 AC) and didn't know the fighter could give him disadvantage with his shield since he hadn't used that ability yet. Even then the second strike would have hit except the wizard threw up a Shield spell raising his combined AC to 22. I felt it was a reasonable risk for the giant to take.
Still, at this point it is obvious that he is going to have trouble getting to the wizard, so using an action to bring back his leader makes sense. He will take an opportunity attack from the ranger, but she isn't a heavy hitter, and he can go around the fighter to get to the other giant. The remain winter wolf should distract the party long enough that he can make it a two giant fight again by next round.
And speaking of the ranger... I gave my party the same items as the ones you gave to the other group, but the bard items really don't fit her. Any chance you could give her different items? She is Dex based and has the defensive fighting style. She switches between a rapier and a longbow in combat. No shield.
And in case it was missed in my edit above. Where should I put my characters? This thread? Or somewhere else?