I'm going to disagree a bit here. Even free foods have the capacity to affect your losses if they are eaten to excess. A mullerlight is 100 calories (and i know we don't count calories but bear with me) and we have heard of people having up to 10 a day. That would be 1000 calories a day on snacks alone before you even add in free foods, superfree foods, HEs and syns. Would it be any wonder if that person didn't lose weight.
That said I don't think 2 a day is eating them to excess. Personally I wouldn't have any more than that and would try to find other snacks - for the sake of variety if nothing else.
The only other thing is that the sweetners in them might irritate your stomach after a while if you consume too many of them!
Could you not replace one of them with maybe some fat free natural yoghurt instead? I have that for breakfast with some canderel sprinkled on top and some superfree fruit in, lovely and sweet and no so many calories.