Final Fantasy VII Remake - Bridal Candidate Outfits

Tifa - By doing all side quest in Chapter 3, you will unlock Discovery - Alone at Last. Go back to your hostel room and help Tifa fix the drains. You will now have 3 choices to make - each will result with different dress in Chapter 9. This means you have to complete Chapter 3 for 3 times and every time make a different choice, complete the chapter, save, then load CH9 and finish that one. NOTE - if you do not do any side quests here and you don't do the discovery, Tifa will be in her Mature dress option by default - that can save you some time.

For Aerith, CH8 determines which dress will she have - finish 0 side quests in this chapter will result with one dress, finish 3-5 for second and all for the best (red) dress. You also need to finish the chapter to change the outcome in CH9.

For Cloud, you can get one dress (blue with tiara) if you do all side quests (Burning Thighs, The Party Never Stops and A Dynamite Body). Do discovery with Johnny in the Wall Market and in parlol go with 3000 Gil option.

Second dress with cloud is by doing the branching quests in CH9:
When speaking with Sam, after you get to entrance of Wall Market, select "She's great at handling books". Don't interract with guy in front or inside of hotel. Do no chase Johnny when you see his discovery event (do not talk with him). When Sam toss the coin, select "Heads". In massage parlor, pick option for 3000 Gil. Answer Aerith with "Looks comfortable". Now do the Colossum main mission and when you unlock side quests, you will get this instead of the others above.
Complete The Price of Thievery and Shear's Counterattack, which will grant you Cloud's second dress.
Last dress - do not do any side quests in Chapter 9, choose the cheapest option in parlor (but it should not matter anyway). This will grant you his black/gray dress.

Final Fantasy VII Remake - Quests Guide

How I see it (optimal guide):
First run - CH3 finish all quests and choose one option for Tifa during discovery event (not the mature one!). Solve all quests in CH8 to get the best dress with Aerith. Do one set of side quests with Cloud in CH9 to get one of his dresses. Finish the dancing contest with Andrea and save. You can now repeat chapters, progress is saved.
Second run on Hard (replay chapters) -  CH3 finish all quests and choose different option for Tifa during discovery event (different from one you did before, but still not the mature one!). Finish this chapter. Replay chapter 8 and do 3 side quests. Finish this chapter. In chapter 9, aim for the different set of side quests for Cloud (check above). Finish the dancing contest with Andrea and save. You can now repeat chapters, progress is saved.
Third run (replay chapters) - You know the drill, do not play side quests in CH3 - that will be mature dress for Tifa in CH9. In CH8 finish 0 side quests and finish the chapter. In CH9, do not finish any side quests with Cloud. Finish the dancing contest with Andrea and save. Done!