How do I kill flowers that keep coming back every year ,that spread li

You will have to dig them up or smother them with heavy black plastic.

Since they're spreading, they are perennial and send seed out after they flower, or they're roots survive over winter. I would try digging or pulling out the newer ones and using RoundUp or a similar weed product on the rest. If that isn't an option, check the labels on weed killers and use something appropriate on them. You may just have to dig them out and start over. Broadleaf weed killers will also kill flowers. Ask the nurseryman if you aren't sure.

I can't use RoundUp or any other poison in my yard as I have cats and also attract birds with birdhouses and feeders. I find that spraying with vinegar mixed with laundry or dish soap in a spray bottle helps, and then I cover the unwanted weed with black plastic trash bags or plastic tablecovers. Weigh down at edges with bricks or what ever you have available and leave it for a few months before peeking. It should smother the plants. Keep checking at the edges for sprouts trying to spread out and pull them out right away. When everything is dead under the plastic, thoroughly dig out the area, removing every shoot or root you see.