I don’t know what
$image = $bank[0]->bank_logo;
is getting, but you can’t get an image field from a related post this way.
Code here depends on what the relationship is returning. I am assuming that you have it set to return a post object
$bank = get_field('bank_institution', $id);
$image = get_field('bank_logo', $bank[0]->ID);
You need to use the ID of the related post to get the field from that post