Kitten Weights & Adult Food?

When should I be switching my kittens to adult food? Vet says after they're spayed (planning to spay at 5.5 months). 

I'm not sure if Cairo is too thin, or if Miami is getting fat, or both or neither, lol, so I'll post some pictures of them so you can see their body condition.

Currently they get free choice dry kitten food (I am planning on adding in wet food to their diet soon, but I am planning to keep it 50/50 with dry) and Cairo gets a tiny bit of hairball laxative once a week because she eats my hair and it gets stuck in her poop and then poop everywhereeeeee lol. I've been debating taking them off the free choice but I'm worried it will make them even less thrilled about being locked in my bedroom (we have a cat/dog situation). 

Miami has been bigger than Cairo since they were about 7 weeks old. They were the same size when I got them at 6 weeks. Their weight gain has been steady and has stayed the same relative to one another. They're up to date on deworming. 


Cairo


This is Miami from the top. 


Cairo from the top. I can feel her ribs pretty easily, but not her spine.


Cairo from the side


Miami from the side.

I don't really know what kittens are 'supposed' to look like weight wise. If they were horses I'd want Miami to stay as she is but not to gain at all, and I'd want Cairo to put on some weight. They are 4 months old.

also it is REALLY HARD to take body condition photos of kittens!

Their weights look okay to me. I wouldn't be worried unless they start looking thinner than they are now. Most kittens are that active they don't tent to get fat. What they eat they burn off in play.
I think it's personal preference when to switch over to adult food. Kitten food contains more vitamins and protein than adult food so is better for them.
I sure others will disagree with me here but I always change mine over to adult food at about 5-6 months. But as I say I think it's personal preference

They're both on the slim side. Personally, l like feeding kitten food because it's typically higher in protein. My cats have 2 canned kitten foods still in their rotation and they range from almost 8 years, to almost 2 years. They're all slim and in good condition. 

lf you like what they're eating, they like what they're eating, and they're obviously slim and active, l see no reason to rush changing - if at all.

Thank you!!

I know they are in good health, but they are my babies and I tend to be a little bit overly concerned about them, especially since I haven't ever raised kittens from this young on my own before.