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?

comparisons to anything in general are simply annoying.

Please do discussion with her. Not so proper compare to other people.

Speak to her that you feel uncomfortable with the comparison.

Talk to her about your side and prove yourself to her

best is mag usap kayo ng mahinahon

Speak directly with her you don't like it

Just tell her not all kids are the same,

oooooooooooovooooooooooooo

Prove yourself to her

Talk to her about it