The weeds look like they may be dallisgrass and crabgrass. The left photo looks like it may be crabgrass on the lower right.
See our website for photos and control information. http://extension.umd.edu/hgic/dallisgrass
The least toxic method of controlling crabgrass is to handpull or dig it out. If the crabgrass is young, you can apply a postemergent herbicide labeled for crabgrass.
To help prevent crabgrass next summer, reseed and thicken up your lawn in the fall, mow at 3 inches, and fertilize in the fall. Next spring reapply a crabgrass preemergent. For season long crabgrass control consider applying your preemergent twice (but make sure the product you choose does not contain fertilizer). Apply first in early spring then again about 6 weeks later. Also see the following publication on crabgrass control. https://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/tt-43e-crab.pdf