Who is being unreasonable here?

Unfortunately I think it's you. We're not talking about a washing machine or a hoover which is pretty much against rules to use at night, but hygiene is a personal and 24 hour thing that you can't really dictate use of.

You kinda make it it out like it's some sort of attack against you, but people just want to use the facilities they pay for. At the end of the day it's not them having a shower that's annoying you, it's that you're a light sleeper and the fan is loud - so I'd look at fixing the fan before trying to use passive aggression to pressure people not to shower.

I'm not trying to pressure them not to shower, I asked if they'd mind going before 11 which I think is pretty reasonable, I wouldn't say showering at 1am is normal behaviour, especially when they got home at 5 and have just been sitting there for hours

Well that's just it, it's not up to you. Wanting to clean yourself when you feel dirty is normal, how they actually allocate their time is again, nothing really to do with you. (I think sending multiple messages trying to dictate shower times is clearly trying to pressure them, and I'm not too shocked they were blanked)

Again, fix the fan, if you aren't willing to spend the time doing that you certainly shouldn't be trying to stop others using the room.

I'm in a rented uni house with 3 other girls and the way the house is laid out, the bathroom has no window and an extractor fan and the extractor fan is in the wall which joins the bathroom and my bedroom, the light and the fan are on the same switch so there's no way to turn the light on without also turning the extractor fan on. The fan is extremely loud and it prevents me from getting to sleep if I'm awake or wakes me up if I'm asleep.

However, my two of my housemates shower at midnight-1am every night, and it generally takes me a long time to get to sleep so after being kept awake until gone 1am I usually won't be asleep until 3, and I have to get up at 7 for lectures and studying so I haven't had more than 4 hours sleep per night in weeks.

I put a message in our house group chat (because we're never all in the same room and calling a house meeting felt too confrontational) explaining the situation and politely asking if they would mind showering before 11pm and all of them have seen the message but only one responded, the other two completely ignored it and then later put unrelated things in the chat so they have definitely seen it.

The midnight showering continued and I have mentioned it with several of them when I happen to see them in the kitchen (just working it into conversation like if they say they're tired I say "me too, that extractor fan kept me awake all night") so they all know full well that it is keeping me awake but are choosing to go on showering at midnight.

I just don't get it though, surely 11pm is a reasonable time to have a shower by (they are not going out/just coming back, they get home at around 5 and spend the rest of the night at home) and if I knew that my behaviour was depriving someone of a basic human need I would be willing to make a slight adaptation. Also, the fact that they know full well but choose to ignore the issue, if they have a problem they should say outright ("no, I'm going to keep showering at 1am, I don't give a **** if it keeps you awake") and at least own being an ********.

am I the one being unreasonable here or are they?
(sorry for the sleep deprived rant)

TLDR: my housemates shower at 1am and the really loud extractor fan keeps me awake, I've asked them to shower earlier but they won't

How am I meant to "fix the fan" when it is inside the wall? And how is my right to be able to sleep any less important than someone else's right to shower in the middle of the night, especially when the issue could be resolved by a small change to their behaviour, which I would be more than happy to make if the shoe were on the other foot. I can't change my routine because it would mean missing tutorials or lectures that are at 9am