Father can't attend due to health issues :( how to honor

Is he healthy enough that he could record a speech and have it played for everyone at the reception? That way it's obvious he hasn't passed, he just unfortunately couldn't attend. Also, if you're not close to your stepdad, can your mom walk you down the aisle instead?

You could have your dad on video chat, and walk down the aisle with the device so that he's still able to have that moment of being with you as you walk down the aisle (and also set the device on a chair in the front row so he can watch the ceremony). I also agree with Jessi's idea of asking him to record a speech, and then play it at the reception.

Since you don't want your stepdad to walk you down the aisle, I would feel free not to have him do that. Walk alone, with a friend, or with your mom (whatever suits you). I love the idea of your dad recording a speech (if he wants to do that) and setting up a way that he can watch the ceremony virtually.

Have your father record a toast and walk down the aisle with your mother. You can also reserve your father a chair in the front row for your ceremony