A great pack of character! The review here is mostly aimed towards Jana as she's the new release, but having never given my thoughts about Skip I figured I should do it as well;
Skip overall is an amazing character, the sprites look stunning and quite adorable if you ask me, on the gameplay side, he's extremely responsive and the dive attack is incredibly versatile just like the one from Odyssey you inspired it from, if I'm not mistaken.
The scrap / monitor mechanic seemed a bit flow-breaking at first, but with experience, it's perfectly possible to collect scrap as you plow through levels by diving onto enemies in the way and then use em up on monitors you need to further better your time and flow on some levels. This mechanic overall is greatly helped by how the dive interacts with shields, and in the worst case scenario, this mechanic can be ignored and is completely harmless!
I'd call Skip essentially perfect for how simple and efficient his gameplay is, being easy to learn, having some intricacies and high skill ceiling thanks to the scrap mechanic which will give you the necessary edge when used correctly and also acts as a safety net for newer players.
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Jana is a character I had a bit more problems with; her sprites are amazing and super cute just like Skip, my gripes come more from the gameplay side.
You here have a character that has an emphasis on mobility, and her wall jump ability shows that. It's quite frankly a bit busted but who cares, it's SUPER FUN to use, it can cancel basically any state making it very lenient which means I was never scared about risking my life above death pits! Coupled with her dash ability to make it even stronger, and you got yourself a speed demon that's super fun to use!
...The thing is, this completely overshadows her other abilities being the cut and the slam. Generally speaking, abilities strictly designed for combat in SRB2 don't work, at least in my opinion. SRB2 enemies are too passive to bother wasting time on them, as a result, I found myself only ever using the cut against bosses and the slam only ever had use in DSZ2, and otherwise actually caused me to plummet to my death because I pressed jump too early when wanting to walljump. I understand the intent of these abilities and see that quite a lot of effort went into the visuals (props for the slashing animations, they look really good!), but unfortunately I feel like they only add clutter and don't often serve purpose.
If I was to suggest anything, I'd move her dash ability to spin on ground, and her slash on mid-air spin (while also adding the projectile to the air slash to make it more versatile), and maybe the slam to tapping spin again after slashing if you want to keep it, otherwise the dash could destroy floors by just skimming over them.
Reasoning behind all that being that I'm a bit on edge about using custom buttons on characters that have otherwise simple movesets that could easily fit on 2 buttons, and the doubletap caused so many accidental near-deaths in my playthrough I had to disable it and remap my custom button to somewhere more comfortable where it still felt awkward to use instead of spin given how often you use the dash in actual gameplay.
She doesn't really NEED ways to defend herself on the ground since she can pretty much avoid any enemy encounter, and I don't think jumping before tapping spin would be too much of a stretch in boss fights since the enemies are usually airborne there, especially if you'd have a projectile to act as leniency on the timing.
Overall, this is excellent work and are some of my favourites characters to use and I'd recommend just about everyone to give them a go for a fresh experience, so keep it up!