We have to make more tags in this community like Natural-problems, plant-difficiencies, etc
Fruit split on pomegranates late in the season is a common problem. Some varieties are more prone to this than others, and many varieties will split open once over ripe, which is part of the natural process of a tree spreading its seeds. Pomegranates growing in arid regions which receive sudden exposure to plenty of rain at the ripening stage also tend to split open more frequently. Some growers recommend supplementing the soil with boron, but the commonest reasons they split are 1) fungal infection and 2) incorrect watering. Fungal infection sometimes shows itself on the tree with spots on leaves and some leaf loss, but it tends to affect the fruits primarily, causing fruit split.
By far the biggest cause though, and one you can certainly do something about, is number 2, poor watering regime. You say your grandfather waters with half a bucket of water every two weeks, which certainly doesn't sound like enough water often enough during a two week period, particularly while fruits are growing. Pomegranates will split if you water irregularly, and will get fungal infection if the roots are kept too wet. which is why you read that drip irrigation is something to try. Drip irrigation will keep the soil damp, supply the fruits with sufficient water as they start to swell, yet prevent the roots from becoming waterlogged.
You can try something else though; once the tree has flowered and fruit has set, when they're small, increase watering to every other day with half a bucket of water, and as temperatures climb and the fruits get larger, every day. A bucket of water is a nondescript term - I'm assuming the bucket holds, say 8 or 10 litres of water. The amount of water required will depend on the size of the tree and how much fruit it's carrying, so to some extent, it's an experiment to determine just how much water is the right amount. The trick is to keep the fruits regularly supplied with sufficient water - regularity is key.
More information on fungal infection and watering here https://www.gardeningknowhow.com/edible/fruits/pomegranate/splitting-pomegranate-fruit.htm