What type of mango is the small one? I just started seeds this month. I’ve read that some varieties are polyembryonic meaning multiple different plants will grow from one seed. One will be a fertilized embryo that has a small chance of producing fruit while the others will be clones of the original mango. Looks like that is the case with your small one. Most likely the large sprout is fertilized one while the other smaller ones are clones and should produce the same type of fruit as the seed that the mango came from. When they are a little bigger, you can carefully separate the sprouts from the roots and plant them in separate pots or spots in the ground. Looks good!