Answer: Because you're new to growing grapes, let me share a wonderful source of information through Washington State University. Here's the web address:
You'll want to download and read the publication EB0775, Growing Grapes. I promise you that this publication will address all of your concerns.
To answer your questions, grapes should be deeply watered once each week. It is normal for some leaves to turn yellow; as long as the vines are growing and healthy new leaves are developing, a few yellowing leaves shouldn't cause any concern. Depending upon the types of grapes you have, there may or may not be a bumper crop every year. Grapes need heat to mature and the grapevine that is not producing may be a different type - perhaps it flowered earlier than the others; perhaps a cold snap affected fruit production - there are many factors, as you will read in the WSU publication. Grapes mature on their own schedule, depending upon type and heat requirements. You'll know when they're ripe by tasting them. I don't expect they'll be ready to harvest until late September at the earliest, but keep sampling them and you'll figure out when they're sweet enough to harvest.
Best wishes with your grapevines!
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