Let me help! Hopefully this will clear it up for you. :)
Is our meetup still on? = this indicates you are asking if the plans you made in the past will still happen. Example: I called John and asked, "Is our meetup still on? I really excited to see that new movie." John replies, "Yeah man, I'll see you soon."
Does our meetup holds good?
Does our meetup holds?
=These two we would not use or say. They are not grammatically correct or an expression or way of conveying a message.
Does our meetup still stands? = Take the s off of stand and this one is also a great way to express your idea. Example: I called John and asked, "Does our meetup still stand? I really excited to see that new movie." John replies, "Yeah man, I'll see you soon."
I would most likely ask someone in an informal way: I want to make sure we are still on for.... (our movie plans tonight) or I want to make sure we are still good for.... (our movie tonight).
More formally, I would say: I want to confirm our meeting is still set for... (the meeting next Monday.)
Hope this helps. Good luck! Let me know if I can help in any other way! :)