I'm sorry to hear about your health problems and I wish you well with your treatment. However, I don't think that I can offer you much comfort with regards to these flights. Given the total price it would appear that what you bought would be their cheapest flights which are usually non-refundable and non-transferable. This is usually covered in the published T&Cs which you have to tick that you've read before being able to proceed to purchase and whether the ticket is refundable or not is usually repeated in any email confirmation of the booking. You need to check back through all the paperwork and the T&Cs on eBookers website.

The obvious thing to do in a situation like this is to claim against your travel insurance assuming you either have an annual policy or took out a single trip policy for this visit when you booked. On the other hand if you didn't take out any insurance then there is little that you can do other than try and appeal to Virgin's goodwill to perhaps allow you to postpone the flights to a later date? Or allow you to resell them ourself in return for an admin fee for changing the names?