TL;DR for what has ended up as a lengthy answer:
- No matter what I say, your opinion is your own and you can act on how you feel. I'm mostly trying to reframe your observations to a more neutral standpoint.
- From your description it seems like your friends are being genuinely themselves, and are not malicious nor particularly targeting you. Their behavior seems perfectly fitting with their age group, where social occasions can be considerably more casual and unplanned than you are expecting them to be.
- How can you know for certain that their standard for reliability is too low, as opposed to your standard for reliability being too high? (I'm not asking for an objective answer here - I'm trying to get you to see that standards are arbitrary and subjective lines we draw).
- Asking others to change should not be the preferred solution.
- There are plenty of ways to work around each other's personalities as opposed to forcing each other to change.
- If you can't deal with them being unreliable, you don't have to. But it may lead to ending the friendship instead of them actually changing themselves on your request.
How can I, politely yet effectively, communicate to each of them that I need them to become more reliable?
While I understand how this affects you, I suggest you take a step back here. It is not up to you to need your friends to behave in a way that is natural to them.
"Oh they are so unreliable it's always the same" although he is acting in exactly the same way 9/10 times
You're all young adults, and it's often said that the twenties are when you start discovering who you truly are, it's the first period in your where you're finding your own way without your parents' guiding hand.
Lack of self-awareness is part of that. It's easier to identify faults in others (when they negatively impact you) compared to seeing fault in yourself. Depending on the person, even when your flaws are pointed out you way still be oblivious to them.
When I was in my early twenties, I can't remember many people my age who planned things far in advance. Most social occasions were decided/planned within an hour of them happening.
It's perfectly possible that your friends are not capable/interested in making long term plans as they play things by ear.
As a general rule, you can talk to your friends about a problem you're having with their behavior, and ask if they can consider how their actions respond to you. For example, you can ask them not to make jokes about a particular topic because it's just not funny to you.
However, I do feel that this particular instance is very close to judging your friends for who they innately are (regardless of whether that will change in the future), rather than trying to address something they're doing. The fact that all three friends show the same trait suggest to me that you are the outlier in this group, not them.
While I am intentionally twisting your words here, it's actually not that hard to rephrase your questions as "how do I get my friends to be better people, like I am?" And that is the core issue: your question implies that your way is better.
So I want to take a step back here and address the difference in personality between you and your friends, without assuming that one is better (or more right) than the other.
There is a difference in personality between you and your friends. Based on your description, you are the only one who experiences this as a problem rather than an observable fact that warrants no further action. There are a few outcomes here:
1 - You accept it and deal with it.
Your friends are not being malicious, nor reckless. This is simply the way they are, and the way they interact as friends. You accept that your friends are unreliable and thus never truly rely on them, but you don't require them to change and simply avoid situations where their unreliability would negatively impact you.
2 - You ask your friends to change.
While this is a viable option, it should not be the go-to option. You must first consider how justified your request is. How can you know for certain that their standard for reliability is too low, as opposed to your standard for reliability being too high?
Even if so, if you're going to ask them to treat you differently, are you willing to endure the consequences of being treated differently? This can often lead to resentment, a quid pro quo assumption that you also change your behavior, or quietly being kept out of the loop on some things. While you may be okay with that - you might come to regret that as well.
At the very least, if you do talk to them, present it as an incompatibility rather than their misbehavior. Address the problem ("I relied on you to drive me to the shop because I need groceries") as opposed to the people ("You said you'd drive me to the shop and you didn't").
Be open to the possibility that even when they are willing to change, they may be unable to change. And that should not be counted against them, especially if they tried to accommodate your request.
3 - You don't accept it.
You can't handle unreliable people and thus no longer hang out with them.
On a personal note, one friend in our group (we have been friends for 15+ years) is still notoriously unreliably well into his thirties. Makes plans but doesn't follow through, cancels just before an event, no-shows without cancelling, doesn't respond to calls/texts, forgets to call you back, makes last-minute decisison to appear at social events, ...
We all know that this is just who he is, he doesn't mean anything by it and it's not targeted at certain people. Even if we ask him to be more reliable, he would never be able to. Not because he doesn't want to, but because this ties into a much larger emotional instability that we as his friends cannot approach nor fix.
And instead of cutting out someone who is still a good friend, we have simply adapted our expectations of him. We often joke that you never make plans with Tom (name changed), but rather that his appearance at social events is a forecast: the more people hear about it from him directly, the more chance there is of him actually appearing. In reality he appears <25% of times when he says he'll come by.
But we don't get upset because we all know that this is the case. We never make plans that rely on his appearance - and if we do, we explicitly stress the necessity to him. From his side, he also makes considerations: if he decides to join a social occasion last minute, he brings his own food/drink.
Two years ago, he said he'd go to a festival with us. Tickets were €200+ each, which I fronted. And he was a no-show. But he paid me for the ticket anyway, so I don't harbor any resentment about it. We knew that it was a possibility from the start.
There are plenty of ways to work around each other's personalities as opposed to forcing each other to change.