The smartest beings on DC Earth would be Bruce Wayne, Lex luthor, Probably Superman, Martian manhunter, Green arrow, Gorilla grod, in no particular order. They all have diffrent forms of intelligence so it is hard to say.
However, I would say that Black Panther is at, or above, Batmans intelegence level in most ways. He is cannon 8th smartest person in marvel.
Reed and Doom are tied or first with Hank Pym somewhere in the top three as well.
In terms of intelegence, i would say Reed and Doom have no equals in DC earth.
You will need to clarify your goals. You said they will have to convince people to their side, but what side? what would Reed and Doom want to do together in DC earth?
I'd say damage wise, without any other Marvel help, Doom and T'challa could work the politics and economy angle and beat out lex luthor in terms of public power. Once they have his resources they take out Wayne enterprise and buy him out. Wayne has too many secret batcaves for them to get everything, but they would get quite a lot of recourses from this enterprise.
With that, they have the recourses nesesary to replicate a lot of suits, probably not the Hellbat since it required a lot more than just tech, but These three would also waist no time learning the magic of DC. Nth metal, atlantian magic, hell, i can see Doom getting a ring of power without even known what one was(Green or yellow, both would work i think). Once they explore these new avenues of power i would be suprised if they didn't make geadjets above Hellbat Tier.
If they had Stark or Pym they could do so much more, but i don't see these three actualy makeing suits. Doom would make drones though, dangorus ones.
I think they could take down the JL at that point, if they wanted. But they would certainly rule the world, or at least the parts that matter, economicaly and/or governmentaly within a year with the only trouble being Lex and Bruce, with notable exceptions being Atlantis and the Amazons, but they too would fall eventually if they allowed team marvel to gather thier forces and continue reaserching the powers that be.