What is the very first fighter jet that pioneers the twin engine and twin vertical stabilizers over the engine just before the exhaust (like the F-14, F-15, F-22, Su-35, etc)?
One of the first was probably the unconventional XP-79. https://en.wikipedia.org/wiki/Northrop_XP-79
It never entered service of course, but does meet your criteria.
Something that kinda meets your criteria would be the F7U Cutlass. Twin tails and twin rear mounted engines though the tails were in separate tail booms outboard of the engines, a similar configuration to that of the DH Sea Vixen and Venom of roughly the same period.
These did enter service.
This also did not enter service.
Probably the MiG-25. Near as I know, it was the first to use the ‘four poster’ layout.
Prototype only: the YF-12A. This was an A-12 derived fighter plane. The A-12 is better known for its other derivative, the SR-71 Blackbird. Both the A-12 and the SR-71 were intended for reconnaissance tasks, but the YF-12 would have been a fighter.
With a first flight in 1963, it beats the Mig-25 by a year.
Possibly might be the WW-2 era Me-262? I believe the prototype had twin tails.