Yeah, any rule of grammar is liable to have several valid alternatives
Roger, of your three websites, I agree with this one:
A second university website said you only append an 's if you pronounce another syllable after the name, e.g. lois-es would then be spelled Lois's, whereas a word like boys would only have a ' appended to it because you don't pronounce the plural, boys-es.
Lois' just doesn't sound right to me when I'm reading... but I'd definitely go with the Kents' kitchen, or whatever... or Lanes' dysfuntions... <g>
But isn't it a great sign that we've not only got people who know some grammar, but we've got people who *want* to know more? That attitude right there is, I think, a big part of the reason that we have such high quality fanfic.
PJ