Since each donation is "in memory" of someone, is it safe to assume that the list of deceased people is known and limited?
If so you could make a page with a title like "Make a donation in memory of:" and then have a list of all the people below that. When a donor click's the person's name it takes them to a page specifically for that person with it's own list of Paypal buttons in different denominations. When they click any of those buttons it is just like buying an item in an online store - meaning you would get an email telling you how much was donated for which memorial by what person. (Individually created buttons "know" that information)
This means the donors do not have to fill out any online forms (except for processing their credit card through Paypal). If your donors are older, they will greatly appreciate not having to fill out forms and you will probably see more donations.