Just finished my exams (going into year 12) so hopefully I can help...
Eng Lit and Lang are untiered, and a separate English Speaking component (where you speak to your class and answer a couple questions) yields a pass, merit, distinction grade. This contributes nothing to the English Language grade.
Math Foundation tier has a lot less content and requires ~55% for a pass (4) and ~70% for a good pass (5), which is the capped grade. Math Higher tier allows grades 3-9 but has a lot more and a lot more harder content, and about 20% for a pass (4). Higher Maths is aimed at people comfortably in ~6+ attainment (not super strict) and my school was very liberal about forcing students to do a tier, and they took into account what the student wanted as well as parents (this took a big role in deciding science tiers too).
Combined Science: Trilogy (formerly Double Science) studies all three subjects and results in 6 exams, 1h15min each. Foundation has less content and easier content, requiring ~50% for a pass (4) and ~60% for a good pass (5), once again capping the grade at 5. Higher is once again 3-9, with more content and harder content, with ~25% for a pass (4) and ~35% for a good pass (5). In terms of final grades, you receive a weird hyphenated grade such as 6-5, 8-8, or 4-3 (with the higher one first).
Separate Sciences (formerly Triple Science) have a separate grade for Chemistry, Biology, and Physics. In terms of difficulty compared to Combined Science there isn't too much difference, literally just that there is more content in Separate (so will come with more lessons of science a week--I had 8). Separate is also split into Higher and Lower, with Higher allowing 3-9 (~25% for 4 and ~35% for 5) and Foundation allowing 1-5 (~55% for 4 and ~65% for 5).
If you're going Further Education route, then A Level Math generally requires ~6 in Maths, Physics requires ~6/7 in Maths, and all sciences generally require ~6/7 or ~6-6 in Combined Science or the corresponding Separate Science.
Sorry I don't know much about requirements for English courses but i hope I helped a little as I saw some outdated information about the new GCSEs (I swear I could take an exam on how the new GCSEs work at this point), so any questions please ask.