And there it is. The only reason you're against this is because of personal bias of the concept which makes you not see how it's possible because you can't accept such a thing from your own personal perspective of how you would handle such a thing IRL.
That's never going to happen and it doesn't need to either. It's been acknowledged the Jocks did it, the DIKs accept that it happened, and they've bounced back better than ever and don't seem to care about needing any sort of recompense nor should they. DPC's not going to go into that level of detail here.
It's funny here how you start off still not getting the point but then end with getting it but acting derisive about it as though it isn't the answer when it is the answer
Yes, they are both in different area of the party and also on another side of those shots. If you think of the render you're seeing like a person with a camers taking a picture, then the other guests not in shot are literally everywhere else around them; to the left of them, right of them, and behind them. How is this so hard for your mind to comprehend?
Logic, dude. 87 people at this party, the climactic season finale, and just the general context of where the story is at; DIKs and Jocks fighting over the HOTs, animosity rising over this and the recent pics sent to the Jocks. The solution to this isn't separate parties and splitting the HOTs 50/50, a solution which would not satisfy either frat. The solution is a joint party, probably one that is organised for the college at large rather than just one for each frat, so that there's no fighting over the HOTs and to try to ease the tensions by making them cooperate.
I don't give a damn if you think "they can't party/coexist together" because of your own personal hang-ups and unwillingness to accept a logical scenario, because they can easily be made to. Simplest example is Sage giving them an ultimatum, "do it or the HOTs will never party with either of you again". That would easily motivate both of them to set things aside for one night and force their hand into doing it.
Trying to dimissively brush it off as just "standard balloons" and not being willing to accept they're the same because it's the same location and the same color scheme just shows how hard you're losing this argument
It is made up because you are literally making it up

It's like you've never been to a party or a disco and don't know what strobe lights are

And even if it's not that, that still isn't going to be fireworks or Sage looking sad because she's not with her friends in this strange and totally unlikely scenario you've concocted in your head.
Well, let's count:
1. MC | 2. Derek | 3. Rusty | 4. Tommy | 5. Jacob | 6. JB | 7. Jamie | 8. Leon |
9. Nick | 10. Sage | 11. Maya | 12. Josy | 13. Riona | 14. Camila | 15. Lily | 16. Sarah |
17. Melanie | 18. Elena | 19. Heather | 20. Ashley | 21. Arieth | 22. Quinn? | 23. Dawe | 24. Ant |
25. Chad | 26. Caleb | 27. Darius | 28. Alex | 29. Jimmy | 30. John | 31. Jill | 32. Bianca |
33. Carla | 34. Zoey | 35. Nicole | 36. Bella | 37. Jade | 38. Stephen | 39. Philip | 40. Nora |
41. Cathy | 42. Hagar | 43. Troy | 44. Becky | 45. Tiffani | 46. Tara | 47. Kylie | 48. Penny |
49. Gina | 50. Clara | 51. Cinderella | 52. Mia | 53. Erin | 54. Felicia | 55. Leanne | 58. Charlotte |
59. Avery | 60. Lisa | 61. Beth | 62. Celine | 63. Christie | 64. Dani | 65. Minny | 66. Wendy |
67. Suzi | 68. Linda | 69. Micha | 70. Chen | 71. Marc | 72. Oscar | 73. Sally | 74. KRJ |
75. Ron | 76. Lucas | 77. Christian | 78. Gordon | 79. Rich? | 80. Trent? | 81. Tybalt? | 82. Magnar? |
So, as you can see, quite a lot of named characters with the potential to be at this party should it be one that is open to the whole college, incuding faculty. The ? characters are the ones I'm most unsure of even in an all-college party because some may not want to go and Quinn in particular may not be around anymore. But there's still other characters like Alvin, Billy, Brian, Benjamin (if he hasn't been expelled), Benjamin's roommate, Bert, Eugene, the unnamed asian girl that's been at a lot of parties and is in the science class, plus all the unnamed extras that DPC uses to fill backgrounds.
All-in-all, there's a lot to choose from to get to 87 but it's probably going to packed with mostly known and named characters.
Ridiculous and unlikely because it's not something either frat would accept.