For anyone already overwhelmed by all the grammar discussion, it’s okay to read over it, only partially understand it, and move on. The most important grammar will come up again and again, and it doesn’t hurt to ask about previously-covered grammar when it comes up later!
(I know I sure didn’t catch on to a lot of this grammar stuff the first time around…)
Condensed for length
(Typo catch: His line ends with お前ら, which is effectively the plural of お前.)
Your translation is very close. As you may have figured (based on your translation), ズリィ is ズルイ. Saitou is a bit crude in his wording when talking with the kids, so sometimes you’ll see a word turn out different from you’d expect.
「いくら情報が欲しくても」 is along the lines of “No matter how much (the) information is desirable…” The いくら provides the “how much” portion of these.
The second half of the sentence is a clause containing a topic, and a comment on the topic. This is the core of the Japanese sentence structure.
In the topic-comment structure, you state a topic, and you make a comment on that topic.
Topic: ヒーローごっこで警察に頼るのは
Comment: ズリィだろ
The topic is comprised of:
ヒーローごっこ＋で = “playing hero” + particle which in this context we can think of as “with”
警察＋に = “police” + destination particle = “do (verb) toward/at police”
頼る = “to rely on”
=> “to rely on the police with your playing hero”
A topic has to be a noun, so の is added to turn 「ヒーローごっこで警察に頼る」 into a noun. Then は marks it as the topic.
The comment portion is:
ズリィ = ずるい = “unfair”, “dishonest”
だろ = short for だろう = has a meaning like “don’t you agree?” or “you know?”
=> “It’s unfair, you know.”
Keeping the topic-comment structure when translated to English, it wound be something like, “Regarding relying on the police with your playing hero, it is unfair, you know.”
Bringing all of it together (and making it sound smoother in English:
“No matter how much you want information, it’s unfair to rely on the police for your hero play-acting.”
Note that it may be better to translate this as “it’s cheating to rely on the police”.
マトモ means “decency” (among other closely-related English words). Essentially, Saitou is saying that Yui is the only decent kid in the group.
For verbs, you can add づらい to the end to make them into an adjective meaning "(verb) is difficult to do). With a “godan” verb like やる, the う sound becomes い (resulting in やり), then づらい is appended.
The で here I believe is だ (which we see at the end of “a [noun] is a [noun]” sentences). However, it’s in the joining form, で. This allows another sentence to attach on to this one, similar to “and” in English.
I don’t have a good translation for his line here, but I’d say along the lines of, “Just this kid’s decent, and conversely that makes this difficult to do.” Essentially, it’s easy for him to tell off さっちゃん and 琴葉 because they’re bad kids, but his technique doesn’t work the same on Yui.
Thanks for catching that one; I went on a bit long answering that I missed it =(
There’s no limit on how many questions you can ask =D Especially when you’ve put in the effort to glean what you can from the material before asking.