Which group does germanium belong to?
According to the IUPAC, the is not such thing as groups IV A and B anymore.
All the elements you are analyzing belong to the 14th group of the periodic table, each one in one period, from the 2nd to the 6th.

In regards to your other question, you need to look for a trend on the elements of the group.
What happens as you go down the group?
I think you've already figured out that the number of electrons around the nucleus significantly increases, and this has an important effect on the radius of the atom.