Hi Andrew, and welcome to planDisney! I am so sorry to hear about your dad's health condition. I hope everything goes well during his treatment and that he can enjoy his visit to Disneyland with you and the rest of your family.
Andrew, as long as your
tickets are unused, you will be able to transfer them to an August date. All you have to do is cancel your July theme park reservations, which
you can do on the Disneyland website, or through your Disneyland Mobile app. Once this step has been completed, you will be able to make reservations for your August dates and link your tickets to those dates then. Act as soon as possible, as they do fill up fast. I just checked the calendar, and
August has availability for both parks, whether you are visiting one park per day, or if you have Park Hopper tickets.
I hope all of this information helps you today, Andrew! Best wishes to your dad, and that your family has a wonderful visit to Disneyland!
Frances