Most Neolamprologus get too big or too aggressive for a 10g (brichardi, leleupi just to name a few). Shellies (some are neos) would be better. A trio of the smaller species such as the occellatus or pearly occellatus would be nice or a pair of brevis. A sole J. trascriptus or *bonded* pair would also be nice. However, are there other fish in the 10g? They may conflict with the above species.
I agree, there probably is no solution for your 40g. However, a group of peaceful, small tetras would make for a nice set up.