Well, don't want cause a massive OT discussion here, but a consistent part of the Lebanese population is Christian. Also there's a minority of Christian Palestinians. Interestingly enough, 2% of the population of Gaza is Christian.
But, while Dr Kent is right to point out that Arab and Muslim aren't synonims, I made the same assumption that the family in question was probably Muslim, as none of the articles I read indicated their religion, one of the articles mentioned that the octuplets' grandfather is Palestinian-born but made no mention of the family's religion.