The fourth one is Dracaena marginata or the Madagascar Dragon Tree.
It's not a difficult plant to look after but it does hate to be overwatered and that's usually the easiest way to kill it. I water mine every couple of months and make sure the soil is never soggy. It deals with low light-levels quite well and can be put just about anywhere but it doesn't like to be constantly moved or it goes into a "sulk" its best to find it a home and then leave it in that spot.
My biggest problem with it has been small "mozzie" like flies that can live in the soil when I bought it, but I just repotted it up with decent drainage in standard compost with a 1/4 grit and it is doing fine now and no mozzies!

Kate