Kittens dying one by one. Should I take the other kittens to vet?

My cat Rubee gave birth to five beautiful kittens on 6th November. The kittens were very energetic and gaining weight normally until yesterday. I came home from class to find one of the kittens dead. It was disastrous. Another kitten has died today. I don't understand what could be causing this since they are all healthy.
I'm concerned and I don't want the three kittens left to die. Should I take them to the vet for a check up, just in case?
My mum took my cat to the vet yesterday and it was found that she had an inflammation which caused the milk which was producing to reduce. Could this be the reason for the death of kittens?
Should I start using KMR formula for the kittens, just in case?
I'm so confused.

I think that you should start the formula immediately  If Rubee has an inflammation she could be passing this on to the babies and they're not strong enough to fight it.  Also taking the babies to the vet and having them checked out would be very very good thing to do.  And tell the vet what's going on with Rubee and the babies.  The more info the vet has the better for both of them.

I agree with Keyes about bottle feeding the kittens and getting the kittens to the vet (I suggest taking mom and the kittens together, even though mom was seen at the vet yesterday.)

I suspect the mom may have mastitis? This can cause the milk to get infected and spoil. It's also quite painful for mom. What did the vet say about allowing her to continue to nurse?

Very sorry about losing the 2 babies.

You mentioned they were all gaining weight nicely, have you been weighing them?

Unfortunately, many vets are not all that savvy with new babies. I know it seems that they should be, but they often can simply listen to their heart, take their temp, and tell you that babies do die, and there is not alot that can be done about it. They may give fluids.

So the work needs to be done on your end, and the biggest issue is whether they are getting enough milk and gaining an appropriate amt of weight DAILY. 

This is the fastest way of determining that they are or are not nursing enough.

If not gaining at least 6 grams a day then you will need to start supplementing.

This will be done with KMR brand milk replacer, however they will NOT use a bottle as long as they have mom, so you will need to syringe feed them.

The average amt needed is 8 cc's or mls of kmr for every ounce they weigh, per day.

BUT if they are also nursing but not getting enough to gain, then you will need to adjust this amt obviously.

Use a 1 ml syringe (no needle) and have a warmed baby on it's tummy only, head tilted up a bit, VERY slowly drop a couple drops into the cheek area and watch for breathing/swallowing. One drop inhaled is disasterous, causing pneumonia fast and death, so it's critical you take your time.

If they have good sized rounded tummies, and do gain nicely, I suspect the 2 that died may have been a bit smaller/weaker, which means they will constantly be getting bumped off of the nipple, and causing them to quickly grow weaker and finally give up, then die.

By the age these babies are, they have their favorite nipple, and anytime they try to nurse, a bigger baby will fight for it and take it away. 

The bigger babies always get the best milk filled nipples, which leaves the smaller ones with the less desired nipples and lacking food supply.

If you notice a baby start becoming weaker, limp, rub some white caro syrup on their gums, the sugar rush gets them going again and you can start syringing. This can and does save a baby.