I was thinking about how you would construct the sentence and made me go on a tangent on how we use the noun modifier with verbs.
My first instinct was to make it: 宿題があるしてなきゃいけません。
But wasn`t sure if I should make it: してなきゃ宿題をある。
I couldn’t figure our which one it would be or maybe its something totally different idk.
宿題がある would be the natural way to express this if im not mistaken.
Something like 宿題あるでしょう？ would be what you’re looking for I imagine.
Are you trying to imply “you have homework to do, so do it”? Because you need a conjunction in there to connect the clauses.
宿題があるから、してなきゃいけません
(Also, using the casual abbreviation なきゃ plus the polite ending ません is a little odd.)
I agree with @Vanilla about the natural way to express the thought. If you want some suggestions about the grammar issues in your two ideas:
宿題があるしてなきゃいけません。
You would need to add something like ので as a “because” to link the two sentences in here, and also it’s just しなきゃ, so
宿題があるのでしなきゃいけない – “I have homework, so I have to do it”. (Though this has drifted away from what you wanted to say.)
してなきゃ宿題をある。
This is closer to the original English in that it’s trying to modify the noun. But (1) you can’t use that contracted form in a relative clause, (2) the particle to use is still が, (3) してなきゃ is still wrong. So
しなきゃならない宿題がある “I have homework that I must do”
What’re you eyeballing me for? 
you can use bunpro grammar page for free if you have questions how to use a grammar point
https://bunpro.jp/grammar_points/86
‘must do’ / ‘have to do’
Ahh thank you this makes sense, but then I was thinking that maybe just 宿題をしてなきゃwould get the point across. Like the fact you have homework would be implied.
Yep, lots of ways to get the point across. You want しなきゃ here too, though. (This gives you “I gotta do my homework” or something in that region.)