My heart goes out to you both....having a dear friend sick /dying and knowing there really isn't alot that can be done is one of the hardest positions to be in. I was there 4 yrs ago and remember only to well what I felt. The blame at 1st as to what I thought I should have done as to what I shouldn't. Really all you can do is make the best informed decisions you can. If you do them with the friends health and well being in mind , you won't go wrong. Be strong both of you and rest assure you beloved pets know you are doing what is best for them.
