Does that mean that all of the new superheroes are now classed as an Avenger?
I’m not clear which superheroes you’re counting as “new”, but as you may remember, Spider-Man is officially made an Avenger (by means of a very official hand gesture), by Tony Stark on board Obsidian Maw’s ship during Infinity War, so he’s in.
No-one else appears to have joined the team at any point after Civil War — Doctor Strange and Black Panther seem to be defending their own respective turfs, and the Guardians of the Galaxy don’t get near to earth or any Avengers until Infinity War itself, where the only hand gesture they get from Tony is a raised repulsor.
do the accords from Civil War mean no-one is an Avenger?
Nope, given that in Spider-Man: Homecoming, we see Tony ready to announce Spider-Man as an Avenger until Peter changes his mind.
The Accords in Civil War outlaw superhuman activity that’s not authorised by the UN; they don’t abolish the Avengers. The team members who didn’t agree with the Accords and went on the run (Cap, Widow, Falcon, Witch), and those who accepted plea deals to avoid prison (Hawkeye and Ant-Man), are presumably no longer considered part of the team. There’s also Hulk, who seemingly abandoned the group at the end of Age of Ultron.
That leaves Tony, Vision, War Machine, and Thor as probably-active-ish members of the Avengers, as of the beginning of Infinity War.