Titans and Mothers are some of the easiest zombie boss to fight.( for lv 30+) Basic technique is circling around. For Titan, you might need to have at least 60+ agility with decent armor and Endurance. Use pistols or rifles for low aggro killing. If you're pro, use silent melee for low aggro.

For Mother, agility 60+, no need for armor or Endurance (unless you are too careless and get hit). basically stick with a pistol or rifle for low aggro killing. You can use melee first then kill it with pistol or rifle. Since that mothers are slow (due to pregnancy) and they stop moving when they start vomiting at you. So circle around them at first. When they start to flinch, it means that they are about to die. So quickly go back and pull out your pistol/rifle and shoot her until she explode.

This is a image of a Titan. Sorry about the image of mother, because I can only upload one image. :(