My wife always compares my parenting with her sister's husband's parenting and thinks he is a much better father than me. I find this comparison annoying and heartbreaking. How do I make her understand this?

Whatever you do may masasabi at masasabi ang iba. Kahit anong explain mo pa. Di mo kailangan ng validation ng iba to prove that you are a good father to your child. Just continue to do what you do best, be the best father to your child and once na lumaki na sila, sila ung makakaappreciate sa lahat ng efforts mo and it will all be worth it.