herp herp

Ike: Turning out a little above average overall.  Speed is the only important stat lagging behind (by about four points compared to expectations) so keep an eye on it - you need his speed to have a shot against the Black Knight.  It should be fine though.  Ike never fails to be good in the end.

Mist: Get her some BEXP stat if you plan on continuing to use her.  Hell, feed her up to 20 and promote her if you have enough laying around.  She's actually a great unit once promoted, since she can defend herself with swords (get her a forge or a spellcasting sword though, standard swords won't cut it) and evades like crazy, but she'll never get there without BEXP.  Taking on the Black Knight without Mist being personally capable (she'll have to defend herself against generic enemies) is insanely difficult and will cost you unnecessary retries.  Too early to comment on stat growth.

Rhys: Turning out fantastic.  Mind you I still don't think that highly of light magic in FE9 (just doesn't pack enough raw punch) but hey, fine unit.  Might want to start accelerating his growth a bit though.

Soren: A bit hardier but weaker output wise than expected averages at present.  There's not really anything wrong with Soren though.

Boyd: Boyd is already one of the best non-mounted units and congrats he's blessed in his biggest problem area: Speed.  And doing well everywhere else.  If you swap him out I will be very disappointed in you.

Mia: Doing well.  She's lagging a bit behind in Skill and amazingly she doesn't actually have that great of skill growth to begin with, but it's not like swordmasters have problems hitting/criticalling anyway.  And yes she's at like 4 higher RES than expected right now.

Zihark: You're pretty much spot on; those stats have actually been a bit lucky for him.  Adept is boss too.  Doing well.

Nephenee: Pretty much as expected. She's a bit up on skill/speed and a bit down on res, but it's not out of the ordinary.  She's actually got a great speed growth (55%!) so surprise.  She's one of my favourite FE9 units (and is even more nuts in FE10) so... yeah.  Keep her around.

Jill: Being blessed in STR but only about average/below elsewhere.  Unfortunately, don't expect any huge speed jumps for her any time soon.  Speedwings might be in order here if you have any laying around and continue to use her.

Astrid: Jesus christ what kind of pagan gods did you sacrifice to get these stats.  Almost everything is like 4-5 points above what it should be.  Congrats this is the only time I'll ever suggest using Astrid.

Marcia: Your Marcia has also benefited from the arcane rituals because her STR should be like _7_ goddamn points lower than it is right now.  Anyway, Marcia's great, her speed and luck are going to continue to go up which will help save her from that low HP (which is... actually what it should be at.  Pegasus Knights don't into tanking hits)

Oscar: Big blessings in STR, SPD, LUK, and RES.  A bit behind in Skill but eh.

Overall: There's no reason to really swap out any of these characters.  Most of the rest of the recruits are reasonable at what they do, but all your current party members are the "start low end high" type as is.  As for Gatrie and Titania... Gatrie's not bad, but you do have a highly mobile party.  And while Tits is a fine unit, the fact is that from here on out even if she's levelled, her usefulness is going to start dropping while everyone else is just getting better and better.  Entering the second half of the game after chapter 17 is about when Titania starts to become more of a burden, so... yeah.

As for who to use for the space you'll have?  Shinon should join shortly if you want a secondary archer; Geoffrey's reasonably capable; Calill is an option (for fire tome use, especially Meteor, which Soren will be slowed to an absolute crawl in trying to use because HA HA Soren's STR), Ranulf's not bad, Muarim is amazing [seriously just leave the Demi Band on him and watch him tank everything forever].  You could use Elincia too but you already will have two fantastic staff users.