For low pressures/concentrations, it would be expectable that all three are similar: Freundlich can be gained via Taylor expansion from the others and Temkin is in the derivation essentially Langmuir augmented by lateral interaction, see Desjonqueres/Spanjaard: Concepts in Surface Physics (Springer). If the pressure is still low and the coverage is also low, the expectable contribution from lateral interaction should still be weak.

If Temkin and Langmuir match also at higher pressures, that means that the lateral interaction between adsorbate molecules is very weak.

You can try other regretion methods.like Chi square,pearson‘s r instead of R2