No! Chances are this is damage to the main trunks from last winter - inspect the trunks on the yellowing two plants, right up to the top, prodding around to see if there are soft, soggy areas, or anything unhealthy looking. I suspect what's happened is they've been damaged, managed to 'reproduce' so to speak by producing a flower (which makes the seed) and then have given up and started to die back. The new growth at the bottom will take over and you will have multi stemmed plants as they grow. If you find damaged areas on the trunks, they need to be cut down to the base, where the new growth is. This is better done in spring, but if the trunks are really unhealthy, you will have to do it now. If there's nothing obviously wrong on the trunks, leave them on over winter - it may be that you then need to cut those down in Spring.