Replacing in ground skimmers

[PH001]

Hi all,
l am looking for advice on replacing both of the skimmers of my in ground concrete and tiled pool.
One has become detached from pipe below and was loosing a lot of water and the are both showing there age with cracks in each. I have plugged both skimmers to prevent water loss. I intend to replace both skimmers. I have had conflicting advice on whether I need to frame the new skimmers with rebar before setting them in concrete or that it is not necessary? Also should I replace the entire pipe run back to the pump. The existing pipe appears to be some sort of heavy duty flexible type of pipe. I inherited the pool when we purchased the property three years ago, pool is approximately twelve years old. Any other tips on replacing in ground skimmers would also be welcomed.