The two atoms in the functiontionalized graphene are already bonded with the graphene. That is to say, the atomic orbitals (or the molecular orbitals formed by these two atoms in isolated case) of these two atoms may be hybridized with the the carbon atoms of graphene. Most probably, there is no eigenstates involved only with these two atoms. To find out the contribution of these two atoms to some eigenstates, you may first analyze the projected DOS of these two atoms. From the projected DOS, you can get energy position for most largest weight of these tow atoms, and then analyze the local DOS.
For the chemical activity, you may look at the change (increase or decrease) of density of states (DOS) near the Fermi level. More precisely, you may use the methology introduced by the conceptual DFT to analyze the chemical activity.