How would you size the transistors in this problem?
If you have already sketched out the transistor diagrams take the worst case N path (4 transistors if I am not mistaken) and size these to give you the required overall w/l. The other transistors on the N side can be smaller, you have a set of three one of which is already sized from the above. Size the other two to match the needed overall W/L. Finally you have one which acts on its own size that one accordingly.

Repeat the exercise for the P side transistors and you are done.