I really have no context to why these two white girls are controversial. The only actual experience I have of Britain's immigration policy is between 2011 and 2013, and even then I only really heard about how most Immigrants seemed to get a lot of benefits the citizen body didn't, at least in Scotland. They often had better job opportunities and received government (welfare?) checks in a much easier and more timely fashion, and back then I was pretty surprised because 'weird, its the opposite in America.' 

But as for the ex-ISIS people being let back in, I can definitely see why it's a hesitation to allow that, but at the same time if they're british citizens and they'll be punished/reprimanded, it's only natural they receive the punishment in Britain.