I'm not sure whether it's better to first establish characters with the public individually and then as a team or vice versa. You need characters that will serve as a draw to ordinary viewers, and imo none of the most prominent Avengers really even come close to the established branding of a Superman, Batman, WW or Flash.
I know... it sucks ... 🙁
They should give them small cameo appearances in the next few Marvel films.... mention them in passing in Spider-Man 3 .... maybe have Pete try to call them for help/advice... Maybe have Iron Man or Thor do a fly by....have them appear in the newer Spider-Man cartoons, Make a one off feature length X-Men/Avengers animated movie (cheap, but well written to just get them more into the public eye)
They really should have mentioned them at some point in the previous X-Men film...especially Cap
Hmm upon further thought, two Avengers do have relatively global brandname recognition Wolverine and Spider-Man. So they could use them as a launching pad. But that also means in a team show about the world's mightiest, two of the 7-10 slots and most of the airtime would be taken up by streetlevellish heroes purely for marketing purposes.