My friend, you’re talking about one person having some mad urdu skills and the other not able to understand a single word of urdu. The OP clearly understands urdu, but is just not fluent/confident in speaking it. Two completely different situations.
I can speak urdu however my grammer is terrible. I can understand it almost perfectly. However that does not impact my relationship with my husband (was raised here pretty much his whole life but speaks urdu very well) nor my inlaws who speak to me in urdu. Although I agree with you that parents should teach their children urdu, God knows my life would have been much easier! From what I’ve seen the majority of kids know urdu, but just hesitate speaking it due to lack of confidence.