Just an FYI, you don't need to play on your main characters, you can play on a fresh made character and even reset times to repeat for es weapons.
HUnewearl is arguably the single worst character in challenge, she is unable to get the next saber type or gun type in 90% of the stages. (She is basically a shit FO, if you have nofo)
HUcast is by far the best class as omgatpgod. HUcaseal is very comfy as still playable for damage and has access to pew pew guns. FOnewearl is the best FO due to SI tech damage.
The ''best'' team for an easy playthrough usually consists of 2x HUcast, 1x HUcaseal, 1x FOnewearl. But for starter players HUcaseal is interchangeable with HUcast if you want to be pure comf. (Traps are godly in cmode, CT+DT as much as FT get used frequently.)
Other notable classes include-
HUmar: Decent ATP/ATA with spirit obtainable in 1c9/2c4+5, lacks of traps though.
RAcaseal/RAcast: Damage is shitty but they have traps and with specials on weapons they can become a tad better, (fire etc) and if your lucky enough to find and Dim/Shadow/Dark Guns you gonna have some FUN, (Also devils late stages) but these are not especially common.
RAmar: Similar to above but no traps, his ATA is very strong though. He is the only class who can use Railgun from the get go in 1c9 (if it drops).
FOnewm: Not generally great across all stages but he can be super powerful in some stages that have GI/RA techs available such as 1c4,1c8/9 (depending on spawns), 2c4 or 2c5 (this one only if you have FOney as well).
The worst FO: FOmarl,
The worst HU: HUnewearl,
The worst RA: RAmarl.
If the 4 of you give it a go by yourselves instead of being carried I will have major respect, this may be tough at first but even if you finish without achieving S Rank you can repeat stages to reduce times as much as you wish, you will learn more this way and have some good fun experience. I wish you all good luck, feel free to ask me any questions or in the ephinea discord challenge channel, many people there can help out with things.
P.S. I can also help out and carry (with VC) if you are desperate/need help, (if I am not busy with HBR).