The Russos recently
confirmed that Steve lived in a new timeline to old age. And there's no way Steve just sat indoors on his ass in that timeline. He would have saved Bucky and changed history completely with Peggy.
So in a sense, no, they don't give a shit about other timelines changing, as we've pointed out, they've done it several times already. (butterfly effect, every time they visit another time, they irrevocably change it, alt-Cap now knows Bucky is alive, etc). So back to my original point: their time machine is OP and can be used to solve many problems, even if they can't actually change their own timeline. They can bring people and objects across and view scenes they couldn't in their own time.
Related: if an Avenger wanted to find out how Wanda ended up at Westview, just go back in time and stalk her. Lazy writing, but technically possible. I hope the Avengers lose the time machine (or Dr Doom/Reed gets it)