How do i describe overly blind parents without being rude?

Hi! I need help finding the right term to describe parents who are completely blind to their child’s faults, even when it’s glaringly obvious.

If parents only see their child as "perfect," despite evidence to the contrary, what’s a polite yet accurate term to describe their behavior? Something that could gently make them realize they’re out of touch with reality, without coming across as overly rude or condescending.

I’ve tried Googling but mostly end up with terms like "narcissist" or "psychopath," which feel too extreme for this case. I’m not looking to throw around diagnoses, just a word to encapsulate their personality or behavior.

For example, their son has been involved in fights, sold drugs, been violent toward women, and uses psychological manipulation. The parents are aware of this to some degree—they’ve seen his drug stash at home, know he’s lost his license, and have been told about the fights. Yet they deny everything. They call everyone else liars, even those who present clear evidence. They’ll say things like, “Don’t come here and spread lies about my son!”

I’m preparing to have a conversation with them because they want contact with my child (their grandchild). My child’s father, their son, has chosen to cut ties with us entirely. The last time the grandparents were involved, issues arose because of their son’s behavior, forcing me to cut off contact. Now I feel like I need to set firm boundaries again.

I have to make it clear that their son is not perfect and cannot be part of their relationship with my child. I can’t expose my child to his behavior or their denial of it. Either they accept this reality, or I will have to cut contact completely until my child is old enough to make their own decision about whether to have a relationship with them.

Any advice on what to say or how to handle this?