Talk to Pediatrician on Doesnt Gain Weight

My son is 5 years old and he weighs 15kg. He eats well mashaAllah. But he doesnt gain weight. His sister is 2 and she doesnt even eat half much as he does but she is 12.5kg. He has asthma/bronchitis for which he takes montiget sachet and nebulized for. He has a small vsd peri membranous. He is super active and very playful.

As for his diet He normally has two slices of bread and egg for breakfast and a glass of milk. In lunch he has roti and gravy. In evening he has suji kheer or oatmeals And at night rice or roti. He is very picky and does not like to eat unless he is spoonfed. Most of the time he just complains im not hungry. I have given him pediasure from past 1 month but still no weight gain. His weight is like a kg gain each year????. I am concerned and i get alot of negative remarks which make me more fruatrated as a parent.His father was a chubby child and mostly everyone from his father side are chubby i am slim but not as slim as he is his height is fine.