Also currently stuck at Ch 25 Conquest Lunatic, which is a ridiculous pain in the ass. Nearly all of the enemies having Inevitable End encourages waiting to recoup your stat losses, but the soft 20-turn limit makes a mockery of that. A number of factors in my personal situation add difficulty to this: Camilla is currently a Sorcerer so that she can pick up Vengeance and Bowbreaker and is thus basically useless against Ninjas, Niles and Silas don't have Shurikenbreaker yet (but they're close), and Effie is slightly overleveled and therefore can't afford to dip back into General in hopes of picking up Wary Fighter (...Or can she? It would mean losing access to Axebreaker long run, but Aegis/Luna/Pavise/Sol/Wary Fighter General might be better than Aegis/Axebreaker/Pavise/Sol/Wary Fighter anyway).
Also fuck those Lunge Spy Yumi Puppets. Uncalled for, Conquest. Uncalled for.
I'd get Cam back into an Axe-wielding class ASAP, Vengeance and Bowbreaker are just luxuries at this point and she prefers the skills from Wyvern/Malig (Swordbreaker is useful in 26, Trample is OP). If she has S Arthur or Keaton you can make her a Berserker for this map, it might give her enough power to OHKO Ninjas which is very helpful. If you don't have Shurikenbreaker yet on Niles/Silas and you have an extra Paralogue definitely go feed them till they learn Shurikenbreaker (if you haven't recruited Shigure or Kana yet those are good maps to feed on since they are really easy, or if you haven't gotten Nina yet just recruit her and then Offspring Seal to Bow Knight and she'll learn it automatically), that skill makes the chapter so much easier. If you can beef up Effie's Str enough to one-shot Ninjas with a Javelin or Hand Axe that will definitely make up for not having Wary Fighter since she can just kill them on counters.
Corrin can tank Ryoma pretty easily with the Dragonstone+ and some meds if they have enough Speed to not be doubled, he will attack at range so you don't have to worry about stone debuffs. I wasn't able to make the turn limit since I took each side one at a time but a sufficiently beefy Corrin can just tank Ryoma until you open the doors and can run in units better suited to fighting him.
Entrap and/or Freeze staves are effective at handling the Puppets. I like to save one Entrap staff for this map just to dispatch the two puppets on the left, makes that side a lot easier.
If you think 25 is bad, wait till you see 26. :P