Depending on your own beliefs and feelings, you may find that lighting a candle in a church, praying for him or thinking quietly / meditating quietly about him will be of help to you. Without wishing to be harsh, only realistic, he is nopw beyond help and possibly well beyond concern ie he won't be fretting about who has and has not been to see him. Often at this stage and in the condition you describe, the ill person becomes confused about comings and goings in any case. To know he has a card or letter from you and that you are thinking about him will be comfort if one of his main visitors can let him know. Don't beat yourself up about this - your responsibility is to your small children, and your uncle is in safe hands.