What about setting potted plants in there. That way the plants get their rootspace unmolested by the ficus.

The Clivia would probably work well, but do at least dig out a good volume of soil and replenish with new soil to give them a fighting chance. The Calla lilies should have been able to take the conditions, do you water this bed? Succulents such as Crassula multicava and Aeonium canariense var. subplanum also do well in bright shade and handle root competition well. You might also consider things like Ophiopogon japonicus, Carex oshimensis 'Evergold', Acorus gramineus 'Ogon' and Oxalis spiralis var volcanicola. Ferns such as Nephrolepis exaltata also do very well with root competition, as long as they get watered regularly.

It is a problem. As you water to sustain the new planting the fig roots follow the water. I do have Calla and Clivia under Deodar Cedar trees along with lots of Agapanthus, but they are within ten feet of the mature trees. A lawn which is from ten to thirty feet from the trees is almost impossible because of the tree root competition and no amount of water solves the problem. I plan on removing the lawn from this area when I get the strength and decide on a plant list capable of surviving the root competition and the afternoon shade. Al

Try Helleborus foetidus and Iris foetidissima, they both do well in dry rooty shade for me. Also Ruscus aculeatus (butcher's broom)seems happy. None of these are particularly showy, but at least they have interesting leaf shapes. Sue