You should add Blackbeard Pirates as third party. And it confirms that Kizaru's fleets has over 100 battleships.
As for the two parties here,
It's hard to tell how strong Saturn would be. If he is low top tier (Rayleigh) then I could see the Strawhats are capable of fighting the Marines.
It's also match-ups dependent (if Luffy fights Saturn and Kizaru vs other Strawhats then Strawhats loses, if it's Luffy vs Kizaru and Saturn vs other Strawhats then Strawhats wins).
Unless Saturn turns out to be stronger than Kizaru which I highly doubt.
As for York and Seraphims, whoever is gonna gain the Seraphim will turn the tide of the war.
My speculation is that York will get betrayed by WG, then BBP comes in and take controls of the Seraphim.
So the three ways battle between Strawhats, Marines and Blackbeard Pirates will be evenly matched.