The mix of milk and fruits, especially the acid fruits such as calamansi, pineapple, mango and guyabano, is possible only if: 1) a very diluted fruit juice will be used, and 2) artificial fruit flavor will be used.
If we combine natural juice with milk, the resulting mixture will undergo coagulation, the curding of milk due to acids.
As a demonstration, I prepared a dilution of evaporated milk in a 350-ml bottle. Then I squeezed two medium calamansi and mixed it with the milk preparation. After few minutes, the resulting milk curds are evident.
The combination of milk and fruit juice for home immediate consumption is fine. But for commercial purposes, you must invent a technology that prevents the coagulation of milk with acids.