Xander Infernal possible with what I have?

Are you just looking to beat it, or are you trying with a particular theme team for the quest? Either way, show us everything you have, man. I found Ike to be invaluable when not using Armor Emblem.

Is it possible? Probably. Will it be easy? Definitely not.

If you just want to have a shot at winning, tanking and killing each of the horse mages, as well as the sword unit, is crucial. A unit to handle Xander unbuffed is important, and another for the lancer is needed. Black Knight with the proper buffs could hold his own against the mages and sword unit on the right. Myrrh would destroy the lancer and probably could take down the gravity user. A Nowi with QR and TA would probably have the best shot to kill Xander. But seals may be vital to your success. Black Knight needs QR to make his life easier, but vantage worked well for me, and should be able to be buffed to 40+ speed to double everything and its mother after dropping out of QR range (vantage is still a solid alternative, and what I personally used). Myrrh would be strong enough to handle the lancer after Nowi goes in to kill Xander, and Nowi will need at least 32 speed to double along with TA at the minimum. Myrrh would be strong enough with QR and a base kit to kill the lancer and mortally wound/kill the staffer. If you can’t get the buffs for BK to tank and kill then you may not have a chance with the setup I suggested. But if you have a Gwendolyn, even at 4*, and can get her hone armor, you have a chance. Repositioning BK and moving him out of Xander’s range but into the range of both mages and the sword knight will let you have a shot.

Feasibly, you cannot beat the armor, flier, or cavalry quests. You have an outside shot on infantry, but the chances aren’t good.

I can see Reinhardt. Use him to finish off reds. The rest of the team depends on whether you want to initiate or bait on the first turn. If you have someone that can tank both green mages and the red sword unit, then 1st turn bait is your best opening move. Fjorm can probably tank both green mages if she's got two team mates that provide drive res or one drive res and another with fortify res. She should be able to deal with the red sword unit especially since she has atk/def bond. Then she and Reinhardt can team up on Xander. All you need then is a good sword unit to take on the green mages, preferably one with great resistance or with distant def. If you can survive the 1st turn aggression, you can most likely play your cards right to clean them up. If you have a hard-hitting green mage, you can use that to check the blue unit.

You should be able to manage with TBK, Myrrh, Nowi and a healer. I cleared with armor team + hero and TBK was the key. Since you won't have movement type buffs, give your supporting units good defensive spurs and swap (swap is better than reposition on this map). It is a very difficult map but doable.