The first is a non-ornamental yellow flower Portulaca oleracea (common name: Pigweed; Family: Portulacaceae), which is supposedly a butterfly host plant. The 2nd is a white flower weed although I do not know the identity. The 3rd is the common garden weed Euphorbia hirta (common name: Tawa-tawa; Family: Euphorbiaceae).
Some links are provided below for reference: