Oh that is so sad.  I've left my cat at her vet's boarding service a couple
times for just a few days.  Once was for 4 days while I was in DC and one
was for two days while I was moving apartments.  The vet said that the
second time (the 2 day visit) that she was very playful the first night then
she hissed and stayed in the corner the second day.  Which is odd for her,
but she obviously wasn't happy. It sounds crazy, but I told her when I
dropped her off that it was just for one day only.  Turns out, I needed two.
I think she knew I didn't keep my word! :)
I also left  her for 3 weeks while I was in Italy.  She was at home for 2
weeks with a friend who house sat.  Then she had about 4 days alone at home
because the friend had to travel for a job interview she found out about
while I was already in Europe.  She was ok after each time, but she at first
wouldn't come play with me like she used to then she wouldn't leave me alone
to the point where I really almost stepped on her several times  a day.  She
did this after each time.  She's honestly just now getting back to her full
playful self and getting to where she sleeps with me every night again and
I've been back from Italy for a couple months.  I wouldn't leave them in a
kennel ever.  At least put them at your vet's where you know someone plays
with them and they are able to get out and walk around and play and not be
in a cage all the time.  My vet says they board for months at a time for
some people.  But they have two options.  They can board the cats in a large
kitty condo or in a 5 foot by 5 foot cage.  The cages have a litter  box,
bed, food, water, and carpet.  They also let them out to roam the office and
have people come in to play with them daily.  I'm sure your cats will
remember you, but they are probably very sad right now.  I prefer not to
have mine gone from home, but sometimes it's just not safe for them to be
alone for several days at home.  But if they do need to be gone, please take
them somewhere they are familiar with and you know they are getting the best
care physically and are able to be active and play.  My vet is great.  My
cat isn't even afraid to go to the vet or the other office helpers anymore
when we go in for shots and check ups.  She likes them so I don't feel bad
leaving her if I absolutely have to.  Please get them out of the kennel
soon.  I'm sure they miss you!