Rosalina & Luma vs Ryu

Jumping from the edge to a platform is generally safe vs Ryu. Pay attention to Ryu's backair patterns and your own edge timings to avoid getting intercepted or hard read.

If Ryu is hit far enough offstage where he needs to side b to recover, chase him and be prepared to hit him out with backair or downair. This situation is generally death for Ryu. If he is recovering low, a spaced down air will intercept his up b. Up b intangibility ends at frame 6, so anywhere in the middle or end of the up b will be vulnerable. His only aggressive mixup is rising side b (which consumes his jump). Otherwise, Rosalina is not at much risk while looking for an edgeguard.

Ryu can't focus through upair if Luma is alive, and his air speed is very poor. Thus his only real mixup is his double jump timing. Make sure you are spaced and drifting in such a way where even if he airdodges upair, he is trapped and gets hit by a follow-up upair. If you catch Ryu without a jump, Rosalina has the potential to juggle him for his entire stock.

Uptilt and Upsmash also will beat out anything Ryu has, including focus if Luma is alive. Be proactive in maintaining advantage state, as Ryu has very few options to deal with getting juggled by Rosalina.

There is no reason to play without Luma in this matchup. Platform camp whenever she dies until she comes back.

Ryu has a lot of hitlag on several of his attacks. Thus Ryu's moves will stall on Luma frequently. Keep this in mind and avoiding running into the attack after it's already hit Luma. You can use this to your advantage by giving yourself more time to punish any given attack.