I believe Roger only told Garp about Ace. I don’t think Rogue ever told any of the crew members either…

Some of the former members were either retired, didn't know Ace was Rogers son not until the announcement, couldn't get their on time, or some are just flat out dead. They would have probably tried to help if they could in some way, but majority of the Roger pirates wouldn't have access to getting to Marineford. And if somehow they did mangage to get their, it would have probably been to late. IDK, this is what I'm guessing as to why they didn't help.

The only Roger Pirate that I'm 100% certain about that he's still alive (besides Rayleigh) is Gaban, He probably didn't know about Ace being Roger's son

No one in his crew knows that Ace is Roger's son..not even Rayleigh and Shanks..

Here the timeline..after Roger found OnePiece, he decided to disband the crew..at someplace they Dropped Roger and knowing that they will never meet him again..after that Rayleigh continue the voyage to bring back Oden to Wano..soon after that Roger's pirates truly was disbanded and each crew go on their own path..so basically no one in his crew know about Roger's relationship with Rogue..

Garp is the only one know about Rogue and Roger's unborned kid..so yeah, it is just natural if no one of his crew show up at marineford plaza except for Shanks and Buggy..we know how Buggy end up at marineford, but Shanks appearance was quite questionable..I dont think he wanted to save Ace at all..he just somehow was there

According to Ace's manga, spade pirates even met Rayleigh but there wasn't any reaction or intuition about Ace's linage.

Probably only Shanks knew it.

They never know Ace is Roger's son until the announcement. Imagine Rayleigh, Gaban and Nozdon in marineford. Nozdon is even stronger than Jozu.

Are we ignoring Crocus? He fought with them against the Golden Lion at the Edd war.

Roger pirates probably didn't know and besides WB had claimed Ace at that point. Remember WB didn't declare war on Wano or Kaido after they found out about Oden's death. Also Shanks is Luffy's biggest supporter outside of Sabo, yet he didn't personally save Luffy or make sure he was ok. I did find it interesting how Shanks told Buggy to give the straw hat back to Luffy although we knew Luffy was close to death and might not survive.

Anyway, One piece is weird like that sometimes with who helps who

@ASimon24 Thought we were talking bout Ace not Luffy?

@Kamado D. Tanjiro we were. I went on a mini rant. Thats why I made a separate post about it