You don't need to watch them all. Saint Seiya canon in general is large mess but without delving into manga, it can be divided into 3 separate things that can be watched separately.
Original
Saint Seiya (~110 episodes), then to finish manga material about 10 years later Toei did an OVA series
Saint Seiya: Hades Chapter Santuary. Saint Seiya: Hades Chapter Inferno and
Saint Seiya: Hades Chapter Elysion. Not sure if it is or will be acknowledged as canon but currently airing
Saint Seiya: Soul of Gold takes place during the Elysion chapter and to "get it" you'd need to watch the preceding positions on this list.
Saint Seiya Omega is a fairly recently done sequel, set after the events of the original series, with mostly new cast though with a lot of fanservice for older fans too. Especially in the second half a lot of old characters come back and take a more proactive role. You should be okay watching it on your own.
But you shouldn't because it's ~96 episodes of absolute
shiiiiiiiiiiiiiit.
Saint Seiya: Lost Canvas is a prequel to the og series, is not regarded as canon and doesn't require any previous knowledge. Sure some bits, references and callbacks would fly above your head but on the other hand, you will be unspoiled on the outcome which I dare say, will elevate material greatly. The anime is only 26 episodes but it only adapts only the first ~96 chapters of the manga. (out of ~220) If you decide it to give it a shot you will need to go there to finish the story.
Generally speaking, if you want to watch something SS today watch Lost Canvas. As much as my nostalgia goggles would like me to tell you otherwise, Saint Seiya is just not a very good franchise, filled to brink with repetitive scenarios, fights that amount to" get beaten around --->power up through the power friendship/burning your cosmo/"I have to protect Athena !"---> win and poor production values.
LC can't quite escape the trappings of the franchise, it's still shounen as hell and it falls into its own patterns too but I dare say it at least tries. Pretty hard. Story and production values wise, it is way, way above and beyond any other outing of the franchise. If you want to give the Saint Seiya a try and leave with your sanity intact, go for
Lost Canvas