Hibiscus does not need cold. I found it best to use baggie in Soil mix in a warm environment. Those I put in baggie on paper towel did not germinate very well or at all.
Don't know about the others.

I think all those varieties would do better if winter sown. The datura might not depending on the variety. If it's one of the Metels I'd just soak it in water and sow it in soil somewhere warm. I'm not sure if any would do well with the baggie method of germination or not. If you have enough seed why don't you try a few different methods.

Thanks for the responses.
I did throw some in baggies, I will let them sit in the fridge for a week and then take them out for warm germ. I just have this urgent 'need' to see first year blooms, so I wanted to start early!:) I will also WS some.

Yes, the daturas are the metel kind - black current swirl, I did not sow those yet. Are they fast or slow germinating? Is it correct they are fast growers?