Can you put Jeane in your party? She is a rune sage.
As a Support Character you can have her around, but she won't fight.
Anyways, I've just finished my No Grind, Ephraim Hard Mode run of FE8. Party I brought with me to the final battle consisted of:
Ephraim: Got Str screwed early on and had only recently started to turn it around. Caped Skl. Got a paired ending with L'Arachel and a B-rank with Kyle. And ended the game at level 8.
Eirika: Turned out mostly like she normally would but hit a Spd drought right at the end. Got a paired ending with Seth and a B-rank with Saleh. Ended the game at level 11.
Natasha: Got ridiculously blessed Def wise and promoted really fucking early, also managed to squeeze an S-rank out of Light magic. Has a B-rank with Franz. Ended the game at level 15.
Seth: Lost steam at the end but his ridiculous Spd blessing made the Seth bomb a force to be reckoned with even then. Capped Spd. Got a paired ending with Eirika and B-rank wtih Franz. Ended the game at level 19 (thanks to eating a lot of boss kills along the way).
Franz: Serviceable, but nothing thrilling, the fact that he was Seth's wingman and fairly sturdy saved him from the bench. Has a B-rank with both Seth and Natasha. Ended the game at level 11.
Garcia: Got ridiculously lucky early on and built up some amazing Skl and serviceable Spd and Def by promotion which turned him into a mainstay. Capped Str. Has an A-rank with Neimi. Ended the game at level 13.
Neimi: Ridiculously fast, too bad the rest of stats fell behind, if Garcia hadn't turned out as well as he did they both would've gotten benched, though Long Bow access helped immensely. Has an A-rank with Garcia and a B-rank with Colm. Ended the game at level 12.
Cormag: I didn't start using him until the desert chapter and I kinda regret it as he rammed his Str cap and is one of my physically tankier units (although magic makes him its bitch with his nonexistent Res). Capped Str. Has a C-rank with Artur and Duessel. Ended the game at level 9.
L'Arachel: Took forever to promote and really wasn't worth being the backup healer but she did give Ephraim some badly needed support once Kyle got the bench. Got a paired ending with Ephraim and a C-rank with Rennac. Ended the game at level 4.
Marisa: So apparently when you Lethality someone you gain 2.5x exp for the kill, Marisa went from level 4 to 12 in the space of a single chapter (although I may have favored her somewhat given that she also managed to S-rank Swords in time for the final battle allowing me to bring in the S-ranked Sword). Ended the game at level 12.
Gerik: Figured I should bring in somebody competent to replace Kyle and Gerik was solid enough by the end of the previous chapter so I brought him instead, its a good thing his bases are so good. Has a B-rank with Saleh. Ended the game at level 7.
Saleh: Lute's HP total was/is bad so I chose to bring him in instead and he turned out better than his averages, though I really didn't need him in the end. Has a B-rank with both Eirika and Gerik. Ended the game at level 9.
And all the rest of the mainstays who ended up getting benched along the way:
Vanessa: Did fairly well throughout and even got Str blessed early on but she got HP screwed too badly to be allowed near all though dragons. Capped Spd. Has a B-rank with Lute. Ended the game at level 12.
Lute: Did well for the most part but her HP was just too low to afford bringing her to the final battle (not to mention that her Con is so low her Spd was getting murdered by anything above a Fire or Thunder tome). Has a B-rank with Venessa and a C-rank with Kyle. Ended the game at level 9.
Rennac: Took over stealing duties from Colm, though Marisa took over looting duties from him for the final battle, did well for himself though. Has a C-rank with L'Arachel. Ended the game at level 8.
Artur: I really did try to make him usable but Natasha's headstart was more than he could surmount, and he was doing fairly well for himself even. Has a C-rank with Cormag. Ended the game at level 7.
Kyle: He was starting to lag when I finally decided to bench him even though he was a long time supporter of Ephraim. Has a B-rank with Ephraim and C-ranks with Forde and Lute. Ended the game at level 6.
Colm: Last of my regulars for the run and was way behind everyone else in levels (thanks to his lousy Str) but just beginning to pull away from his averages when Rennac showed up. Has a B-rank with Neimi. Did not even get to promote.