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During dormancy, a plant only will need water when the soil is completely dry down to about 2 inches into the soil. This will be much less often in winter, since they will not be respiring near as fast. So the best information is to water as needed.

Just feel down into the soil and make sure that the top is bone dry before watering. This will be the best way to know for sure. If these containers have no drainage (which I do not recommend ever) then this will be much longer in between waterings, since you cannot know when the water is gone at the bottom unless you compare dry weight to wet. Then you can get an idea of when to water in this case.

https://www.gardeningknowhow.com/edible/fruits/fegen/winterizing-fruit-trees.htm
https://www.gardeningknowhow.com/edible/fruits/apples/apple-tree-winter-care.htm

Here are a few different links for you. This one will start you out with apples trees for your area: https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-5/zone-5-apple-trees.htm

This is our entire collections of apple articles that will have lots of useful information: https://www.gardeningknowhow.com/edible/fruits/apples

This website will offer information about each cultivar of apples, and is very useful: http://usapple.org/the-industry/apple-varieties/

Special warm climate varieties of apple trees may be okay. The big issue is getting enough "chill hours" to set fruit adequately to make it worthwhile. You are in a borderline climate even for those varieties. If the temperature stays at 7C range for a long enough time frame it may work. But there may be some years when you won't get much fruit.

Here is a link to the University of Calcutta Horticulture Dept. and a faculty list with emails and phone numbers.

http://www.caluniv.ac.in/academic/department/Horticulture.html

This article may help: https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-8/zone-8-apple-trees.htm

Here are two articles that should help:

https://www.gardeningknowhow.com/edible/fruits/fegen/fruit-tree-grease-bands-applying-fruit-tree-grease-gel-bands-insects.htm

https://www.gardeningknowhow.com/edible/fruits/apples/pests-affecting-apples.htm

Unfortunately, your photos did not come through. It will be very hard to say what is wrong without seeing the damage.

This could be due to many reasons. It can be fungal/bacterial infections, nutrient toxicity or deficiencies, pH imbalances, or insect damage.

Here some articles that will help address some of those concerns:

https://www.gardeningknowhow.com/category/edible/fruits/apples