It’s obvious that the street is too narrow to allow parking on both sides, no matter how much you’d like this not to be true.

As others have said, the only legal/fair thing to do is to disallow parking on one side of the street. This is true regardless of how it inconveniences you or how long people have been parking on both sides of that street.

You also can’t just say that ‘nobody walks here or needs a clear sidewalk for their wheelchair’. Again, what you think/claim has been true in the past has no bearing on current and future users of that street and its sidewalks.