I had seen a few people bummed about not being able to split screen two safari tabs. Chrome and Firefox support split screen so you can still have two windows open.
That's indeed not possible with those internet browsers you are mentioning. There are apps out there which do have an option to show multiple websites at once within the app (so not using Apple's Split View) this can used on various iPads (old and new ones and in some cases even iPhones) see also in the bottom of this topic.
If you also are looking for a browser that has this feature and support the iPad Pro I think there is only uSurf Universal as far as i know.