"Ma" only sounds like "maw" with a southern (and by southern, I mean south of the Mason-Dixon line) accent. In reality (a little something I like to call NORTH of the Mason-Dixon line), they are not the same. "Here" and "hair" are most assuredly different, with the word "hair" taking on the sound of the word "air" with an extra "H" sound to begin with, whilst "here" is like the word "ear" with an "H" sound. However, "here" and "hear" are homophones.

In the word "heir," the H is silent. I don't know why, but it is, apparently.

All of these are assumed that you speak English without an accent, which is perfectly possible.

For those of you who don't believe that there are four-way homophones (because none of the ones mentioned thus far are four-way homophones), there is:

Too
To
Two
Tew

"Three" and "free" are not the same; one starts with a "TH" sound, and the other with an "F" sound. I could not find two sounds more unlike the other.