I wanted to know all the characters from Negima that are still alive and are in UQ Holder. I saw a few such as Ku Fei, Yue, and some cat lady that followed Fate.
Ku Fei and Yue are not known to be alive during the time of UQ Holder. What you are referring to is a flashback scene regarding a tournament that the main characters are now training for. It shows that Yue and Ku Fei competed as a duo in a previous running of the tournament, some time after Negima but, by their appearances, long before UQ Holder.
Evangeline is alive, and serves as one of the driving foci of UQ Holder. She's not quite a main character, but she is a major character that motivates the primary main character.
Fate Averruncus is alive, and currently serves as the primary main character's antagonistic rival. He does not appear to be an active villain; the main character just wants to be stronger than him.
The cat girl you reference may be related to Koyomi, as suggested by Torisuda. Their personalities don't seem to match, so she may be a descendant of Koyomi, or simply another member of the same race of demi-humans. Maybe Fate just likes cat girls, or it's a bit of nostalgia, or it's a coincidence, or any number of things. She hasn't been a significant enough character to be sure.
Also alive is Mana Tatsumiya, the half-demon gun user. She is the one that introduces the main characters to the aforementioned tournament. Since Mana does not appear to have aged significantly, one assumes that other half and full demon characters, such as Zazie, are also alive, but they have not appeared or been specifically referenced.
Negi himself is confirmed as "alive". We don't know his exact state, but he is in some state of needing help/rescue, but not one that is especially time sensitive. This state is what drove Fate into an initial villain role, but eventually they held him off long enough for the protagonists to learn his aims and to negotiate a cease fire of sorts. Since Fate's goal was not especially time sensitive, he did not actually need to press it as strongly as he could have.
No other characters from Negima! have made confirmed appearances. We can conjecture a couple more, at least, in addition to demons such as Zazie. Many fans think that UQ Holder occurs during the timeline where Asuna had not come back: if so, she is "alive", in the sense that she is serving whatever purpose it is that had her separated from the world for so long. Asuna's lineage was also stated to be an exceptionally long-lived one; she was already quite old, technically speaking, when Nagi encountered her. When Asuna did finally finish her task, she found out that her best friend Ayaka had lived well past 100, in hopes of meeting Asuna again. Since UQ Holder is set approximately 80 years after the end of Negima, it is plausible that she is alive.
And we can get a little bit meta: UQ Holder is a society of immortals, several of which we know are well over one hundred years old. Thus, though they may never have appeared in Negima, technically speaking they were alive during the course of its events.
At the end of chapter 95 we see an elderly Ayaka make an appearance, showing off her pactio card, and accompanied by her (presumed) granddaughter, as well someone who appears to be Chachamaru. The fact that her pactio card is still functional tells us that Negi is in some sense alive. This is in much the same way that we knew that Rakan's functioning pactio card meant that Nagi was alive. We also see the granddaughters of Konoka Konoe. I'd guess they are less than 10 years old, and they can recall stories of their grandmother about Negi, so it is possible that Konoka is also alive, or only recently deceased. They specifically wonder why Tota shares their last name, which possibly foreshadows that we will learn about this, and that it is not simply a coincidence.
In Chapter 112, we see two more characters, both of which are immortal or have long lifespans: Sayo Aisaka, the ghost girl; and the demon Zazie Rainyday (in full jester get-up). We also basically get full confirmation that Negi really is alive. It is also confirmed that the Chachamaru-like character accompanying Ayaka (see the preceding spoiler) is, in fact, Chachamaru.
I would just like to say it's also possible for some of the "regulars" to have become immortal along the lines as Negi and Eva had become, or even from Eva biting them (or others like this, not just vamps aka peeps like Kotarou might have made what's her name the girl, he stays with the younger and hey, maybe even the older one into weredogs/werewolves).
Heck, to get meta, other than the class rep, we don't know if any others even aged. I hope they didn't. I am re-reading the first series after years and I'm getting depressed that most of them aged or died, so I hope since it's too late for the class rep, at least the others especially Nodoka, Yue, Asakura, Setsuna (well, she's like what's her name so she's probably immortal), Makie, the twins. Well, pretty much all, but if not at least, the ones more important if he had to, he could make the ones like the food girl that's nice and a little chubby, no offense, but yeah, not a very important character.
But hey, so to answer I will refer to them by descriptions sometimes, and "probably" mean they haven't made an appearance or I don't remember, but, well yeah, probably, but those who are for sure alive are: class rep, Kaede, Eva, Asuna, the ghost probably she didn't move on yet, probably the twins, probably Chao, Chachamaru or the robot, probably Zazie, almost for sure Setsuna, and well frankly, if the class rep who is one of the oldest is still alive, then probably is everyone else.