I'm sooo sorry to hear you're having such a bad time with your cows and your vet.
As a mixed practice vet, I see all sizes of animals, but nobody should feel like they are second best or that the vet doesn't know or care what is happening. I certainly agree with the general sentiment to shop around to see if you can find a more helpful/caring vet.
Firstly, with second stage labour not progressing, and down cows, this sounds like a problem with low calcium. In the run up to calving, a lot of calcium is taken out of the cow, and the sudden demand for calcium to contract the muscles for calving, and for milk production means that the cows can be short.
One of the best ways to counteract this problem is to reduce the calcium in the diet in the run up to calving (the last few weeks), by giving rougher forage and keeping concentrates minimal, even adding in straw to the diet can help. This makes the cow start producing the hormones that release calcium from the bones and diet, so that she is ready to access as much calcium as possible when she needs it at calving. This will help you next year, as you can discuss (probably with your local agricultural/feed merchant rather than your vet who doesn't seem to know too much about cattle) the best regime for building up to calving.
This year, you are probably going to have to treat individuals and minimise the effects. Firstly, when the cows calve, you can give calcium at calving, it can be given into the vein if they are really weak or down, or under the skin to give a slower release. A local farmer should be able to help show you how to do this if the vet can't really help you.
An alternative is boluses, and a lot of farms will give a bolus over the throat which dissolves slowly in the rumen releasing steady amounts of calcium. If you are struggling with calvings that don't get going, it may help to give calcium before this happens.
It may be that the weather has affected the amount of nutrients in the grass and is causing cows that would normally manage to be unbalanced in terms of calcium and magnesium. Sometimes low magnesium in the blood can also cause cows to struggle, so if they are not responding well to calcium supplements, it may be worth having a bottle of magnesium on standby as well. This goes under the skin only, if put into the vein it can slow the heart enough to stop it if given too quickly, so safer to put under the skin.
Hopefully some of this will help, and make calving a bit smoother for you
All the best
Suzanne