Reintroduction process having ups and downs

Hi, everyone! We have three adults cats who have lived together peacefully for the last four years. Out of the blue about five months ago, two of them got into a massive, fur flying fight out of nowhere. We really aren’t sure what caused it.

The third cat who was not involved in the fight (our only female) is best friends with one of them and they are usually together. Though, during the reintroduction, she doesn’t participate in meal time because she’s not food motivated at all, and she’s barely play motivated. Her reintroduction to the other cat will have to come a little later.

The two cats who fought can eat in the same room together perfectly fine and even have a little play time together afterward if they are both playing with separate toys. But during the day, they are separated by a baby gate, where they still hiss/growl and try to swipe at each other sometimes through the gate. They each get time during the day being swapped so they each explore the house as they please.
I feel like we’re making progress at dinner time, but going backward during the day with the hissing and growling when they are separated by the gate.

It’s been five months and we have seen some progress, and we have hope since everyone got along together for a few years, so I know they can do it again.
Does anyone have any advice to help with getting along during the downtime before meals? Should we have a lunch and dinner mealtime? Any advice for this process is appreciated, we just want everyone to get along again, or at least be civil.