This is an amazing shot! What you've found is a pair of dew-drop spiders (Argyrodes sp. in the family Theridiidae) also known as dewdrop spiders. And these two are in the process of mating. The one on the right, with the smaller body, is the male and he's inserting his pedipalp (the dark round bulbs) into the female (the one on the left with the large body).