Hi Vi -
Lactulose will prevent stools from becoming too hard but once the hard stool is already formed, it won't work to soften that stool. That is why the enema is generally necessary at frist, and then starting on the lactulose should help prevent recurrence of the problem. I'm guessing the reason the lactulose isn't working is because the dose is too low at this point. This is a big cat at 14 pounds - You could go as high as 3 ml three times a day.
I would not recommend trying the children's suppositories. Cats are not people and they are so sensitive to so many things that people can take. It is just not worth the risk.
Diet is always a difficult thing to decide what to do for these cats. It is good that you are adding water to the food. Some of theses cats do better with a high fiber diet with the theory being that the fiber draws fluid into the colon and helps keep it soft, while others do better on a low residue diet, meaning that once the diet is digested, there is less volume of stool to be excreted. Unfortunately, this has to be a bit of a trial and error situation to see which works for each kitty. I have had better luck with the low residue diets. Both of these are something you can get from your vet.
I'm not a big fan of the raw diets - I know there are people out there who believe they are the best options, but I think the risk for infections from things such as E. coli and other bacteria are just too great. I think most
Let me know if you have other questions. Good Luck!