Also grains should be part of the diet well a cockatiels diet anyway.I feed my birds green beans but not all the time.Both my tiels weigh 94 grams.

A lot of the "seeds" we give our birds are actually grains, like millet, oats and canary grass seed. Other grains like wheat and corn are basically more of the same - the exact nutritional content varies, but it's not going to supply the nutrients that are missing from seeds.

The green part of the bean isn't what supplies the missing amino acids - it's the "seed" part of the bean. You basically need legumes (peas, lentils, the type of dried beans that we use to make soup) to go along with the grains like corn and bird seed. To make it more complicated, most of these legumes need to be cooked to eliminate natural toxins, but some are OK if you just sprout them.

The "true" seeds are things like sunflower and safflower that have a lot of oil in them. Their nutritional content is closer to nuts than to grains like millet and oats.

There's a different thread going about how to make a bird happy. Part of the answer is to feed a diet that's well balanced to help keep him healthy, but also to provide many different types of food so eating is interesting and enjoyable. Feeding nothing but pellets might or might not be the best way to keep him healthy, but it's definitely not the best way to have a "food is fun" experience. So my recommendation is to feed a significant amount of pellets but offer lots of other healthy foods too.

if seeds in bulk have added vitamins, they won't sprout. At least this is what I was told.

The vitamins are sprayed on the shell so they probably wouldn't interfere with germination. If anything they might serve as fertilizer lol.

The problem with spraying vitamins on the shell is that birds don't eat the shell, and they have dry tongues so very little of the vitamin rubs off in the bird's mouth. They're not going to actually consume much of the vitamins.

so does it make sense to buy with vitamins or not?
store also told me that they don't add sunflower seeds in the main seed mix (that has vitamins) because birds won't be able to crack the shell.

It doesn't make sense to buy vitamin-enriched seeds because the birds will get almost none of the vitamins. But vitamin-enriched is easier to find than plain.

Sunflower seeds are too big for budgies but cockatiels can handle them pretty easily. Sunflower is nutritious but very high in fat, so the quantity needs to be kept fairly low. Some seed mixes have way too much sunflower, and some people deal with it by buying a mix with sunflower and another mix without it, and combining them.

Or you could just pour some seed into the birds bowl and if you think theres too much sunflower in their bowl take some out and put it back in the bag easy.