It's hard to tell.
I think the Emperors are almost equals. Young Whitebeard was stronger, but his older self is on the same level.
In the manga, it's stated by Buggy that Whitebeard was known was the "strongest man" because he could fight with Roger to a standstill. But he got weaker because of his disease.
The current Emperors are supposed to be more-or-less equal. That's how the Emperors system works... while Blackbeard's bounty only half of Kaido, if he was really much weaker, he would have failed to keep his title.
Whitebeard briefly clashed with Shanks. Shanks managed to stop Kaido. Big Mom fought Kaido for 2 days. That tells me they are equals.
It's also hard to judge how the Admirals compare... you can't take power levels in One Piece too seriously. Going by the war in Marineford, the Admirals could keep up with Whitebeard. I assume the same would apply to all Emperors: if they went with everything, they could smash Akainu to the ground, while injuring themselves in the process. But they could never fight the Admirals one after another, like it happened to Whitebeard in Marineford.