Bad gas and softer stool

Hi there,
I have posted a couple threads , just dry food, sneezing and coughing kittens. Well the latest is our two kittens have really bad gas. They will be sitting on our lap or couch next to us and all of a sudden very bad smelling gas from them. They were born in April and are sisters. I am not sure if one or both have it. Also I have noticed softer stool again not sure if one or both.
After two weeks with us I switched there dry food from Science Diet to a grain free one. Also I started after a week or so with us onto Wellness Kitten and wilderness blue kitten canned wet food. They were only on dry food the science diet kitten when we got them. I wanted to add some wet which I give about 3 tsp to half a can a 3 oz can to each in the morning and the dry is left out all day. They do tend to go to each others plate so one may eat more than the other.
They still sneezing quite a bit and some coughing type gagging.
They seem to eat fine, play a lot so not lacking energy at all. They are only indoor kittens.
Anyone with any advice would be helpful and appreciated. I am really not sure if a vet appointment should be made. If they were not so active and stopped eAting I wouldn't hesitate to take them in.

Adding a probiotic and digestive enzymes is always a good idea when switching foods. What grain free dry are they on? If it is blue buffalo wilderness it maybe because of that brand. A bunch of us had issues with their food recently and my kitten al had bad gas when she ate it as a snack (http://www.thecatsite.com/t/258997/blue-buffalo). I think it is just the dry food that causes issues but someone found mold in their canned food.

The dry food is called Merrick whole health made right. Grain free healthy kitten. They were on Science Diet Kitten when we got them and about a week when home. Then I switched them to the brand above as it was grain free and the same price as science diet but more.

It is probably the food change as it is best to do dry food changes slowly. I advise getting a probiotic and digestive enzyme. 

Oh okay. I got a problem with the dry food( kicking myself actually) when I changed the dry food I didn't think as to where I could buy it and so I have only found it at one local store no where else sells it. What makes that a problem is I went into the pet valu store to get kitty litter and though I would take a look at how much they had of the hard food as I will need it in a week or two. They are out and said they only ever carry a couple bags. I am a bit concerned if I needed it and they didn't have it that I would be stuck! I have already changed their dry once and would hate to do if again on them! Which I had of changed to one that was available in multiple stores, sigh, I am right that changing again would not be good? I left my name and number so they could call me when it comes in, if they remember to call!