It's not that you have less context, as much as you /need/ less context. Instead of a few extra words to describe something, you get a different character.
In the above example all three are read as おば (pronounced: oba). When spoken you still need to differentiate, but it'd either be obvious from context or you'd just explain it manually.
Here's a great example of how in writing you can disambiguate "aunt"/"older woman": https://twitter.com/MaggieSensei/status/765769637372030977
In the above example all three are read as おば (pronounced: oba). When spoken you still need to differentiate, but it'd either be obvious from context or you'd just explain it manually.