Mine are not in the ground, but in larger containers. The Mauritius lychee is in a self watering container, the mix is sand and pine bark with some compost. Amendments used Sea kelp powder, Chelated Iron, powdered rock phosphorus, and liquid compost tea. I usually use diluted amounts about once every two weeks during warmer seasons.
The 'Kohala' longan is in a pre made container mix, with mixed in pine bark. Similar fertilizing schedule. I don't like the consistency of the soil, and will replace it soon though (breakdown over time). Longan did produce a crop of about 20-30 medium sized longans, its in a 15 gal plastic container.
I wish I could give you some info with in ground trees, hope I gave you some helpful info.
'Mauritius' Lychee in 18 gal SWC
'Kohala' longan in 15 gal.