Just like English sometimes conjugates the verb differently based on the subject (e.g. "I fall" but "He falls"), German has a different conjugation for each possible subject:
ich falle, du fällst, er/sie/es fällt, wir fallen, ihr fallt, sie/Sie fallen
Here the subject is "Die Blumen," so we use the "sie" (third-person plural) form "fallen."
wondered if you could say "die blumen sind fallen"?
No, you can't.
Or in this case is "sind" not needed?
Adding sind here would be simply wrong.
Like saying (for example) "The flowers do are falling."
Saying that "do" is "not needed" in that sentence sounds a bit as if you could add it if you want to -- but you can't; adding that unnecessary helping verb is simply wrong.
Same with adding sind to die Blumen fallen.
Also, please pay attention to the correct spelling -- Blumen is spelled with a capital B.
What is the difference between fållen and fallen (with the umlaut and without)?
fällen is to fell, fallen is to fall :)
fällen is the causative verb: "to cause something to fall".
For example, Er hat den Baum gefällt. "He has felled the tree." (= He cut down the tree, causing it to fall.)
It's most commonly used with a tree as the object in German, unlike English, where you can also, for example, "fell a man with a single blow" (i.e. knock him down, cause him to fall and possibly die).
"The sky is falling down" means something in the lines of "the sky is crashing down/crumbling down" - as if it were a ceiling of a room or a roof of a building. The same cannot be said about flowers. "The flowers are falling down" simply means that someone/something has put put the flowers on a higher surface/place and now they are falling down, for example "The strong wind blew the flowers up in the air and now they are falling." (in this particular sentence you could, of course, also say "and now they are falling down/back down" but it won't mean that they are crashing down/disintergrating like in the case of "the sky is falling down", it would simply mean they are falling back to the ground.
Unlike the English "are" the German"bist" can only be used as the main verb -- it stands alone and is not used as an auxiliary verb to form a more complex verb structure , e.g. present continuous -- The flowers are falling = Die Blumen fallen. But, "the flowers are fresh"=Die Blumen sind frish.
What's the difference between "die blume sind fallen" and "die Blumen fallen".
The main difference is that die Blumen fallen is correct, and die Blumen sind fallen is not correct.
German does not have a continuous aspect (with "to be" and -ing), and so the English present continuous tense "(they) are falling" and the present simple tense "(they) fall" would both translate to the German present tense (sie) fallen.
English makes a distinction between something that happens regularly or repeatedly (present simple tense) and something that is happening at the time of speaking (present continuous tense). So to speak good English, you have to think about the aspect of the action, in order to choose the correct tense, and if present continuous is appropriate, you have to add that "are".
To speak good German, you don't need to make this decision -- it's simpler as there is just the one present tense.
If a German speaker thinks that an aspect should be expressed, they can do so with adverbs, such as immer (always) or gerade (right now).