When you have a weedy and unattractive lawn with different grasses wanted and unwanted growing the best thing to do is to kill the whole lawn with roundup grass and weed killer and start over. Once the lawn is dead you want to rent an overseeder machine with blades in the front to cut through the thatch down to the underlying soil with a seed hopper on the back of the machine which has seed feeders that run down discs that run directly into the slices cut from the front blades down to the soil below. You must crisscross your passes to seed thoroughly. spread starter fertilizer, lime and gypsum over the whole lawn after.