Solid foods can be suitable as long as they are the right consistency though building up gradually to big chunks. Chunky food out of a jar or chunky food that's homemade are the same food, okay not really lol, but the same stage in terms of consistency. If he can eat crackers and cheese then he can eat your other kids food just mashed up so he can gradually get used to lumpy and then chunky foods. Fingers crossed he keeps improving for you. The reduction in milk and off the bottle will probably make the world of difference too. With a greater appetite hopefully he will be keener to eat solids making life easier for you and happier for his tummy.