Translation:Our mother's sister's husband and our mother's brother's wife are our mother's in-laws.
It seems the word bank for this sentence is too big for my screen, and I couldn't see all the needed words. For example, sometimes I couldn't see "brother" anywhere. If it hadn't been for the option to use keyboard, I wouldn't have been able to complete it at all. Might be a good idea to keep that in mind when giving such long sentences.
I, too, was originally really frustrated with this and similar sentences. I did some fluency drills with the vocab (and used the handy chart one of the mods shared in another comment thread) and I'm really at ease with sentences like this now. These examples do a good job of illustrating the maternal/paternal differences - they help more than they initially seem to. You'll get there! Keep practicing!
Actually, one's mother's siblings' spouses are also her in-laws; that doesn't apply only to her husband's family. If your sister gets married, is her husband not your brother-in-law, rather than your brother?
It's true that this is a very complex sentence, in English at least, and it threw me the first time I ran into it, too. But it's actually both very challenging and very useful to be able to translate both ways (English to Klingon and vice versa) in the long run. Just be glad Marc Okrand didn't decide to add extra terms for elder and younger aunts and uncles and their spouses, too, as some natural (Earth) languages do! :)