I think you need a good diagnosis on the car, a second opinion. Take it to a shop and get an estimate, if you can. You're just guessing here and could be in for a big job only to find it was not the ball joints.
FYI, you don't want to replace just the ball joints anyway, you do the whole control arm. A neighbor tried replacing just the ball joints, and the replacements were a little too small and didn't fit.
Good luck with it.
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