Sibling Rivalry?

Question
Hey!  I'm sure you get questions to this effect a lot --I've read some of them by googling--I just need to ask in regards to my own so I feel better.  I'm sorry if this is lengthy, but I want to make sure anything that could be important is mentioned...
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I'm a new rat owner; last week I adopted two rats from a local pet store, feeder not fancy.  I thought they were cuter, liked the idea of saving them from being lunch, and like the idea of them growing bigger. (My cats like small things, but in the last few days they've doubled in size from mouse-size to small rat-size so my cats are afraid of them now.)  They're about 6-7 weeks old.  I had adopted the two of them being told that they were both girls, but one since has become a boy overnight (you know how rats are,) so now they're each living in separate 10-gallon tanks until I can get him neutered.  (Their names are Milly and Wolfwood, named after characters in a popular anime.  I'm a geek.)
They each are fed every day, this general hamster/gerbil/rodent blend of seeds and things, they have Hartz natural unscented pine bedding, edible logs, and Milly has a small gerbil wheel she likes running in while she's small enough to fill it.  They're well fed and taken care of, and are handled very much (we love our pets.)  They probably spend a good quarter to a third of the day riding around on our shoulders as we go about our business, running up and down our arms, crawling around our shirts, etc.  Wolfwood loves to snuggle.
When I can get him fixed, I was planning to move the two back in together because it's not easy keeping space for the two tanks and they seem to miss each other, (Milly is anxious, Wolfwood is lethargic; we give them supervised time to play together too so they can see each other, but we make sure no rat babies will come about.)  Around this time, because of their growing rate, I was planning on buying them a larger cage anyway (I had one in mind that my friend Sam had,) I believe it was something like 1.5 feet across, 1 or 1.5 feet wide, 3 feet tall (it had different levels they could climb to.)  I thought that way they would have space to grow, they wouldn't need to fight over not having enough room, and I wouldn't have to worry about something happening with the aquarium lids, (if the wire netting broke and the cats got in, for example.)
That's probably more background information than you'll ever need, but I like to make sure to cover all my bases.
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Sam had bought a rat who was pregnant; she raised the babies very well, raised them together until they had to be separated by gender, and raised the genders together.  she found homes for all but two, two un-neutered males who had always lived together and seemed to get along.  They were both close to six months old, which I've read is when they start really hitting puberty and issues can arise.  She said earlier this morning she had seen them cuddling playing, and then recently went to check on them and found one bouncing around and the remains of half of the other.  She was very upset because she thought they always got along.
I can think of reasons why this could have happened--they were both un-neutered males, they were at that age, and for two-three weeks before hand they were not with her and could have been improperly cared for which could have left them malnourished or affected their behavior.  Still, I wanted to double check.
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(Finally the question!  Sorry...)
Would it be safe to have Milly and Wolfwood living together, even if he was fixed and they had a larger cage, as long as they were always well fed, cleaned after, handled, used to each other, etc.?  He's always been the calmer one, but sometimes when she plays with him she tends to be the friskier one-pulling his tail and ears, pouncing on him, etc.  I know right now she's just being gentle and playful, he's never been hurt by it; still, I can't help but have flash backs to my childhood gerbils trying to kill each other when we had to split them up... And now with Sam's rat siblings eating each other out of no where, I'm a tad bit worried.  I wouldn't want to finally spend the money to fix him and buy them a huge cage, and come home to find out that her playing got too rough, she yanked off his ear, and he bled to death... or some other horrific half-a-rat-remains scene.

If she turns out aggressive, is there a way to calm her down?  Will it be safe for them to live together, or am I going to have to keep them living separately with only supervised visits?  =\r

Thank you for your time, sorry for the ramble/excess information...  If anything can help or would matter, I want it out there.

Answer
Hi Kira,
Forgive my answer for being more brief than your question :) I'm 9 months pregnant and I find it hard to sit still for massive lengths of time so I tend to provide short answers and short explanations rather than going into technical detail (I explain this so that you don't think I'm being snappy or rude, I swear it isn't personal!)

Their seed mix is decent but should be supplemented with a kibble/lab block diet; as 90% of the seed is fattening and/or unedible, and you'll find they won't eat so much of it. If the main ingredient in this food is any sort of Hay, you're wasting money and should just switch diets. I personally prefer Mazuri diet for a quick, pet-store bought food.

Pine is HORRIBLE. It causes severe respiratory illness and should be discontinued immediately. If you like to use a wood chip, use Aspen, its much safer than pine or cedar. I also use a recycled newspaper bedding (Yesterday's News or Carefresh, sometimes Cellsorb).. and as another alternative, even plain, white copier paper shredded, or paper towels.

Now, as for your rivalry question.. most likely the reason Sam's boys flipped out at each other was indeed because they were of "that age" and had hit puberty, which is when aggression usually escalates. Sam may have missed warning signs, and perhaps the boys were in a cage too small for adult males to be sharing. The odds of this happening between Milly and Wolfwood (after Wolfwood is neutered) is VERY slim. Females generally don't get aggressive the way males do, I've only met one who has - and she was only aggressive after she was bred. I wouldn't worry about it, honestly. I'd go ahead and schedule his surgery and plan on keeping him separate for two weeks after (to wait for his lil swimmers to die), and then pair them together. Most likely, they'll be fine!