First of all, there's a myth about not touching baby birds. While there's no need for you to get "involved", the myth really has to do with sickly babies who are booted out of the nest by the mother. Nature tells her not to waste time/energy/food on a bird that will not survive. Well-meaning humans put these weakling birds back in the nest, and the mother boots them out again...leading to the "I touched it, now she won't" story. The truth is, healthy babies who somehow fall out, can be put back in successfully, although there is a risk of attack by parent birds who see humans too close.
That said, she's probably feeding them and you don''t know it. She's "sitting on them" to keep them warm, and that's fine. If they are alive, and if she is continuing to come back to the nest, they are fine. And, frankly, if they are all not fine for the same reason (some disease or something), there is nothing you can do about it. Frustrating but the reality of nature.
Yes, they are tiny - but tiny birds have tinier babies. We had a wren build a nest inside an open feeder of ours, and I couldn't believe the size of the eggs! Seems impossible that anything could survive that - but they do!
Since you don't know what the mama bird eats, it doesn't make sense for you to put food out. And what food? Some birds are seed eaters (finches, cardinals, etc. - but within that group, some come to feeders and some are ground feeders) but others are meat eaters (woodpeckers, robins, etc., that eat worms and insects). You live in a lush area in a tropical latitude, so there are abundant food sources available in both categories.
I'd leave them alone, set up a Go Pro camera from a distance if you are seriously wanting to see more, and hope for the best.