I'm still a newbie at this, but take at look at the trees that have mulch, versus those without. Those with mulch look much greener, with new growth. The ones with grass all look bad. I'lll take a close up pic of some of the leaves later.
The soil is likely the same throughout the yard. They all receive the same amount of watering.
The ones with mulch already will have the mulch pulled back from the tree to let it breathe. The ones that have grass will have the grass pulled up by hand (not that big of deal, avoids any chemical or burning from plastic issues), and I'll use the same red mulch use in other areas of our landscaping. It's marked as being safe - no toxic dyes.
Went by Rockledge Gardens last night to buy more mango fruit (maybe out in a week), and to confirm our order of two mango trees. While there, we bought a variegated pink lemon tree that my wife has always wanted. The Glenn & Zill mango trees should arrive later today. Saturday I'll make a trip to Home Depot to pick up more mulch, fertilizer, etc.
In the meantime, I did a dance in the yard when I spotted a mud snake (harmless):
Part of the fun of living on a tropical island!