acceleration of both the disc must be same since there is pure rooling
and friction on smaller disc will be downward and on the bigger dics it will be upwards(Newton's 3rd law) and both will be equal in magnitude.
therefore, writting the equation for bigger dics, f(2R)=2R²/2*(alpha)
since the smaller dics has friction (f) as well as a external force due to which it is accelerating with 2m/s² and the external force was unknown initially. But now it also be found by writing the equation for smaller dics and putting f=2N.
"sorry my previous answer was wrong"