Author shouldn't beat himself up so much about the names. Tomme and Johnne aren't actually too far off from what I'd expect from cognates of the original names and I could see them happening in Europe. John itself comes from Yohanan of Hebrew origins as a theosophic name praising god which at some point came to become a name for toilets when it crossed over into English. Johan, Juan, Ivan, Yahya, Jean - they all are cognates of John so Johnne isn't as bad as he seems to think.