This appears to be white clover (Trifolium repens), which can have white or pink flowers. White clover is an introduced perennial species. The plants with the yellow flowers are black medic (Medicago lupulina), an introduced annual species. Both are common weeds in turf.

Likely the easiest way to control these plants is with an herbicide. There are several lawn herbicides that are effective against controlling broadleaf weeds like these. 

Example lawn herbicide active ingredients for postemergence applications that are selective to control emerged dicot/broadleaf weeds:

• 2,4-D
• quinclorac
• dicamba
• mecoprop
• triclopyr

Examples of products include, but are not limited to: 

• Scott's Turf Builder Weed and Feed
• Preen Weed Control
• Bioadvanced Season Long Weed Control for Lawns

If there are just smaller areas, I would recommend spot treating with Ortho Weed B Gone Chickweed, Clover, and Oxalis Killer, as the active ingredient triclopyr has been shown to be more effective against tough to kill broadleaves in this setting. 

It is critical to read and follow all labeled instructions when making pesticide applications to ensure maximum efficacy and human and environmental safety. 

After you have achieved your desired level of control the work isn’t over. You need to do two important things. 1) Make sure you have a robust/vigorous stand of grass in your lawn to create a competitive environment for weeds. Practices could include re-seeding areas where the grass stand is thin, fertilizing the grass (early-spring and/or early-fall), watering when conditions are dry, and increasing your mowing height (~3.5", this last one will not help with tall fescue but will help with broadleaves and stress management). 2) You need to be on the lookout for weeds emerging from seed. Some weeds can linger as seeds in the “seed bank” of the soil for decades! Controlling these weeds could include the use of a preemergence herbicide (e.g. products targeting crabgrass control) or manual removal of emerged plants. More information on lawn care from the MSU Turfgrass Team can be found on the following website: https://www.canr.msu.edu/home_gardening/lawns/

The active ingredient in Tenacity is mesotrione. That is only rated at providing 'fair' control of white clover by the Turfgrass Weed Control for Professionals guide produced by Purdue University Extension, so it would not be your best option.

Please let me know if you have additional questions.