Duolingo is just picking the word closest to the word you typed. Y'all has two l's at the end, like will. The first bit of the sentence is an address, and the last bit is the main sentence.
Also, take a look it at the prefix, Su-. That's the second person plural subject/no object prefix, so it has to be "you (guys) will jump" or "you (guys) jump" or "you (guys) jumped".
Notice the comma before SuSup, in this case torg and mara is a vocative, they are being called out SuSup is in the indicative mood, not imperative, so it states that "you (plural) jump" not the command "torg and mara, jump!".
It should have been "yunz," since Duo is from Pittsburgh. "Y'all" is said south of the Mason-Dixon line. "Yunzes," "Yunz guys," and maybe "Yinz" should also be acceptable.
The list of correct alternatives does not contain "y'all" but only "you all".
Accepting "y'all" where an alternative has "you all" is an automatism by Duolingo.
If you consider this a bug, have a look at https://support.duolingo.com/hc/en-us/articles/204728264-How-do-I-report-a-bug- .
The initial Su of SuSup is the plural you. But it's not an imperative (apparently covered later in the course). SuSup also covers past and future tense: You jumped; You will jump.
We are teaching Klingon, not English. If someone enters "y'all" as part of the translation and uses it to show that they correctly understand the Klingon, then we should accept it. Unfortunately, Duolingo will occasionally pull those sentences out to show you. There may be a couple sentences where "y'all" was actually entered as a possible translation and as we find them, we'll remove that. Hopefully the contraction of "you all" will continue to be accepeted, but not shown as a possability. There shouldn't be any more problems with this sentence.
I think "Torg and Mara, you will both jump" should be accepted as an alternative. For more than two listeners, "you will all jump" should be accepted. This is how English expresses second person plural.
English has many ways to express second person plural, depending on the area :)
As a general rule, this course accepts "you", "you all", and "you guys" as second-person-plural pronouns, and the system automatically lets you contract "you all" to "y'all".
So "you all will jump" is accepted.
I can add "you will both jump" to this sentence, but in general, if you want to use "all", your best bet is to put it right after you" rather than after an auxiliary such as "will".
You may report additional combinations if you wish on individual sentences, but it may be easiest for everyone if learners adapt to the Procrustean course rather than the course contributors modifying thousands of sentences to add an additional second-person-plural pronoun.
Because that's how Klingon does it. Noun conjunctions come after the list of nouns. In English we put it before the last one (which seems natural to me as an English speaker, but illogical if you really think about it), but in Klingon it always comes last. There are also sentence conjunctions and they come between each sentence.
I don't mind y'all being an accepted answer. But I think if "you" was acceptable, then "you" should be what we see when we get it wrong, given how broad the audience is.