More recent update here (sorry for Daily Mail link):
Father of girl killed in Portugal plane crash slams pilot | Daily Mail Online
Seems to suggest engine failure, not structural failure. Given then it has landed along the length of the beach (as opposed trying to make it out to sea having been flying over land), I can't see a situation where engine failure alone would prevent ditching in the sea, rather than on a beach with people on it. From the article, it also appears there were more people than the two killed on the beach who saw it coming and got out of the way.