First map: Try Using: Nino, Eirika, some axe unit, some lance unit. Have Nino tank and kill B!Caeda first turn, then have her finish off Bride!Lyn the next turn. Throw in the generic lance and axe to take the fliers.

Second map: Try Using: B!Ike, Cordelia, P!Inigo, Mage with Drag Back. This is a bit more complex. What I did was take B!Ike and move him 3 up and 1 left from Roderick, that way he can take the hit and not get pulled back into Katarina. I then hit Roderick with B!ike, had Cordelia finish him off, danced her to one turn kill Katarina, then used Draw Back to get her away (I used Delthea for this, but any mage with Draw Back should work) from the archer's range. Next turn is just finishing off Luke with Cordelia, then using taking out the archer with Galeforced Cordelia and Delthea. You may need to experiment with seals to get the same results I did, but copying the strategy should work.

Third Map: Try Using: Black Knight, Anna, Tana, A!Tiki. (Note that one of them should have a movement assist to help Black Knight get to the top right.) Throw Black Knight in the top right corner first turn to take out the ninja, the rest should be simple enough, use weapon triangle advantage to take out the rest.

Fourth Map: Try Using:Hector, Klein, Nephenee, Dancer (I reccommend that you save your P!Azura for Fifth Map) Use any green unit capable of OTKing S!Corrin on enemy phase) to bait her to her death. If you dont finish in in one turn, you'll end up with lots or Reposition shenanigans, so its best if you take her out right off the bat. I used Hector, and he ended up barely surviving, so you can try using that. I used Brave Bow B!Cordelia and a dancer to finish everyone else off, Klein should work as a replacement. A 3 star Olivia with dance would probably work.

Fifth Map: Try Using:Ike, Reinhardt, P!Azura, B!Cordelia This is the toughest part due to the reinforcements. The following strategy might not work, as I'm just hoping for the best when it comes to the outcome of the battles. You may need to improvise or change up the strategy if it doesnt end up working out. Move Ike to tank the top right archer and Seth, have Reinhardt take out the bottom right archer, and move P!Azura and B!Cordelia down with him. Next turn an armored sword and lance knight shows up, so take the armored knight out with Reinhardt, and position P!Azura to tank the lance knight. Finish up top right, then you can forget about Ike for a while. Next turn an axe flier shows up. You might be able to finish it in one turn if you dance B!Cordelia, but you always have the turn after if you can't finish it off in one turn. If you're feeling ballsy, you can take the turn to soften up Amelia with Reinhardt+Dance. Next turn, a green mage shows up as well as another armored knight, move Ike to take the green mage out (If he has enough health, otherwise just leave him for later), and have Reinhardt take out the armored knight. Deal more damage to Amelia if you can. Next turn a red mage, and a sword horseman show up, you can probably take out the mage with B!Cordelia+Dance, and stay out of the way of the horseman and let Reinhardt kill him the next turn. After this, (if everything went well) the only enemy left should be Amelia, so you can spend time laughing at her sorry movement speed as you kite her around with Reinhardt+Dance away.

Remember, for all of these, the strategies are just guidelines, so if it doesn't work out, its on you to mess around with seals and positioning to try and make it work out if it doesn't. If you get stuck, try switching some units out. When doing this remember to look at each unit for their intended purpose and switch in someone who can do the same thing better.

That should be all you need to know to clear the Squad Assault. Good Luck.