The OP’s letter does not provide enough information for an adequate response.
She says her adult children are underachievers, which means they’re capable of doing more than they’re doing.
That doesn’t sound as if they’re poor readers.
Yeah, my guess was gonna be too much weed, but it’s too vague what the problem is. I don’t how you can raise more than one child and not have the foggiest idea why they have a lack of drive.