The most toxic holiday plant is the poinsettia. It kills dona-hey cats every year & makes lots of children vomit &/or get diarrhea. If you must have them, maybe they should be in a case or on a shelf nothing but really tall humans can get to..
As for holly - if you have a heart condition, it's more dangerous than if you don't, but I don't think there's any record of fatalities from it anywhere on Turtle Island. Europe's holly is different from Turtle Island's holly, but their plant isn't imported here.
Mistletoe will clean you out, but it's tough to kill an adult human with it - although the upset to your innards may make you wish you'd just died & been done with it.. Kids & pets are smaller, so more susceptible, of course.
I wouldn't know a "Jerusalem cherry" if it bit me.. Has it got another name?
I'm glad we Traditional Indns don't have these plants to contend with when we celebrate Solstice.