For chapter 1 - Start the battle by upgrading your Cat Wallet, when enemies come near your castle spawn few meatshields and Axe Cats, they will be your stallers. Meanwhile upgrade your Cat Wallet to max level. When Baa Baas and Pigge comes, let them progress towards your base. When they are close enough, start sending out meatshields, Axe Cats, Gross Cats and Bird Cats. If you want to speed things up, use your Cow Cat and Fish Cat.
For Chapter 2,3 - Send out few Wall Cats and upgrade your Cat Wallet to max level. When Baa Baas and Pigge comes, spawn your stronger units ( Mythical Titan Cat , Lizard Cat etc.) along with meatshields.