Dogs emotionally attached to owner

Question
Hi.  My husband and I have a standard poodle puppy (9 months old) and a flat coated retriever puppy (10 months old).  Both dogs are from shelters.  The poodle had Parvo when we got him, and my husband was the primary caregiver nursing him back to health.  Both dogs are very emotionally attached to my husband.  

He travels at least once a month where he is gone for several days.  Each time he is gone, they continually search for him, whimper at night while we should be sleeping, and appear to be grieving for him.  I have discovered that leaving a couple of shirts that he has recently worn around the house comforts them.  They like to smell them, and it seems to calm them.

Is this normal behavior?
Will they outgrow it as they realize he always comes back?
Is there something I can do differently to make the separation easier for them?

Answer
Well giving them his clothing is a good idea,so they don't think he has left them,sometimes it helps if you walk them and play with them,as that can tighten the bond between you and the dogs

each time it will get easier,and over time they should get over it-also having him ignore them a day before and day after he leaves/comes back will also make it easier on them