It might be that my answer comes too late, but a procedure for computing the nucleolus for three person games can be found at

https://math.stackexchange.com/questions/1108449/finding-the-nucleolus/1109149#1109149

The theoretical details of this approach have been discussed in the book

http://www.springer.com/gp/book/9783642395482

A Matlab toolbox for doing computation and checking properties of TU games can be found here

http://mathworks.com/matlabcentral/fileexchange/35933-mattugames

Using this toolbox one can find the nucleolus by

>> nc_v=nucl(v)

nc_v =

13.5000 13.5000 13.5000

>> B0_balancedCollectionQ(v,nc_v)

ans =

1