Let the simplest one be a), ortho be b), meta be c) and para be d). I have confusion between ortho and meta. How to compare their acidity?
Taking the case of ortho and meta in which you have confusion:
The acidity of aniline will increase if there is a electron donating group in the compound to stabilise the conjugate positive acid formed.
Since OMe is shows +R and -I effect, it is a net electron donating group as +R effect generally dominates over -I.So in case of ortho it is able to show electron donating nature due to +R effect which makes it more basic than the meta isomer which shows electron withdrawing effect due to only -I effect as +R effect will not affect from meta position.
According to source the pKa values (of the conjugate acid) are:
compound °C pKa Aniline 25 4.87 2-Methoxyaniline 25 4.53 3-Methoxyaniline 25 4.20 4-Methoxyaniline 25 5.36