I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
Those yucca plants are connected at the bottom near or below the soil line. There is not an easy way to thin it out. You'll have to put a long handled shovel with a sharpened edge in between plants as best you can and hit down on it to sever the plants apart. Pre-pruning the sharp leaves will definitely help. I suggest pruning the leaves on the plants that you are removing so the remaining plants are left unblemished.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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