New GSD to the family (already have one also)

Question
Hello!  My girlfriend and I got an all black AKC-registered GSD when he was 8 weeks old.  He is about to be 7 months old (will be on 9/17/06) and weighs in around 80 pounds.  He is not aggressive in any way shape or form towards myself, my girlfriend, or her 9 yr. old son.  He is an outside dog and has PLENTY of room to run around.  He will bark at night at passing deer and any movement in the bushes that he may be concerned about.  Once he even alerted us to a snake in the front yard, barked and barked until we saw what he was barking at.  He has a slight problem with cats.  Well, we have 2 cats now.  We had five, gave away two of them, and he actually killed one a few months back.  We were not home and they are outside cats due to living in the country (mouse patrol).  The feline was just a kitten at the time and we had them safe from the dog, but let them out to run around for a few minutes and he got one before we knew it.  I am guessing he was playing a little too rough and unfortunately killed it.  He was about 4 months old then.  The cats are now inside (just 2 of them) and occasionally Kaiser (the GSD) comes in with us for a few hours.  He does not bother the cats unless they try to get near his food or rawhide toy.  At those times he will nip at them.  Other than that, he lets them climb all over him and 'knead' him (they have their front claws, so that surprises me because I'm sure it hurts).  Is this normal for a GSD?  I read in a GSD book that they don't like cats.  The cats are not my main concern though, that is next.
 We recently (yesterday actually) got a 1 yr old GSD (saddle color) from the local shelter.  Toby (the new GSD) seems to be a good dog.  He does not look to be mixed with anything.  He is typical GSD traits, erect ears, shorter hind-end, tail that swoops up at the end.  I would venture to say he is pure-bred, but no way to tell.  The tag at the shelter read

"Good dog.  Good with women, children, and other dogs.  Very afraid of men."

 It took a little coaxing to get him to come to me, but he is fine once he does.  I am wondering how to fix that problem.  My other concern is tonight we had him in our house with us and they were both laying around.  My girlfriend and I were on seperate couches, Kaiser laying in front of me, Toby in front of her.  Kaiser is partial to me, and after tonight I know Toby is VERY partial to my girlfriend.  Lisa (my girlfriend) called Kaiser over towards her, and when he got close, Toby growled and leapt at Kaiser.  He got a mouthful of fur and other than a yelp from Kaiser, everything was ok.  He did it two or three times, only when Kaiser would get close to Lisa.  If she corrects him, then Toby is ok, and Kaiser can come in close and she can pet them both at the same time.  When Kaiser is moving quickly towards her is when Toby seems to be tense.  I do now know the reasons why Toby was turned in to the shelter.  However, judging by his fear of men, I assume he was beaten, or his female owner was beaten which may explain his protectiveness.  The only time Kaiser has gotten protective was when Toby came near his food bowl.  Water bowl is fine, they have shared one with no problems, but food seems to be a problem with Kaiser, and Lisa seems to be a problem with Toby.  Is this something that I should be very concerned about?  I understand it needs to be corrected, but I do not know how to go about doing that.  Any help would be greatly appreciated.

Some personality traits of Kaiser (if it helps):
7 months old, 75-80 lbs.
Shorter than Toby, but "thicker"
Very energetic (still young though)
Not overly protective of anyone
Stays near the house when we are home, lays in front of the front door, barks at passing animals
Walks in front of us (needs correcting, I know)
Pulls on his leash in front of us
Does not bite at his leash though
Stays closer to me than Lisa or her son, but does not have a problem with anyone getting close to me
Seems to not like any animal coming near his food (however he shows NO food aggression towards humans)
Plays well with Toby under normal conditions (no food around)

Some traits of Toby (name change coming soon):
*He is new to us, but this is what I've noticed*
1 yr old, appx. 72-75 lbs (seems a little underweight right now)
Taller than Kaiser, but not as stout
Stays closer to Lisa and her son than me, BUT will come to me if I call his name and clap my hands quietly
Shys away quickly if I raise my voice at Kaiser
Plays well with Kaiser under normal conditions (no food around)
Has no problems with a leash and walks next to us, not in front
He came running out of the woods with Kaiser and stopped next to me, whereas Kaiser passed me
Does not show food aggression towards humans
Have noticed some tensing when Kaiser nears him while he is eating
That's all I have noticed thus far (we've only had him 2 days and he came from a shelter so I don't know his past)

This morning I fed them both and had to seperate them while they ate.  Before they were seperated, Kaiser and Toby got into a tussle and Toby seemed to win although Kaiser is technically bigger.

Please help with any information you can.  There is a lot of info here, please answer any questions you can and give as much advice as possible.  If you have any questions, PLEASE email me and I will respond as quickly as possible.  Kaiser was a gift to me  

Answer
I tend to see dogs as individuals, and not peas in a pod for a given breed.  I must admit it is much more common for a GSD to be highly bonded to one person.  It looks to me like Toby has been through a lot and despertely wants somebody to bond to.  He has sorted things out, you are Kaiser's, and Lisa is his.  He doesn't want Kaiser stealing Lisa.  

It is important to understand a problem.  It is the first step to solving it.  It could be given a few more days, Toby will accept Kaiser's attention to Lisa when he sees that it does not detract from her attention to him.  Have you obedience trained Kaiser?  Likely Toby needs it.  The key to most behavior problems is approaching things using the dog's natural instincts.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/  Regardless of how much training either has had, work them together.  Change off who handles which.  Both dogs need to understand you and Lisa are the top dogs, and accessible to all the pack members.  

As a shelter dog, Toby is neutered or soon scheduled?  If not, it should help.  Likely no good reason not to do Kaiser too.  You don't want him taking off to the far side of the county everytime a female comes in season.