Wow that really sucks, I'm so sorry for ya.
Back in January I had to make that decision to put my pup down after 14 years, and I got him when he was 7 weeks old. For a long part of his life moving here from wisconsin he was all I had for a long time.
Fortunately (hard to say that) I decided to take him in on a Tuesday, and thank goodness I didn't have to. Dunno if I could have done it. The night before I laid on the floor with him for hours after getting home from work and I'm so grateful he passed naturally in my arms. Cripes I still get teary eyed thinking about it.
I'm sorry man, they're such a big part of your lives, and it's terrible we have to lose them.
My condolences bro, be strong.