Most likely, the seeds do not contain the proper bacteria, since that would have been confined to the roots. I'm not sure if adding the proper bacteria is even possible, since most legumes have a specific bacterial strain which has adapted to that species. You might try adding a mixture of nitrogen-fixing inoculants, should you wish to order them... or if you have clover or vetch with nodules, try incorporating some carefully dug & washed roots.

For question #3, probably not. There are many reasons for sickly plants, especially in pots - and tropical plants are even more delicate. Over- or under-watering, poor soil nutrition, inadequate light, and temperatures lower than the plant requires, are just some of the possibilities.