Housing rats together NEED ADVICE

So I have a rattie who is 8 months old (Daisy) & a rattie who is 4 months (cheerio) & Cheerio is growing out of the cage she is in so I need to move her into the bigger cage with Daisy. I tired housing them together once before and they were fine during the day or while the light was on but once I turned the light off they were squabbling more roughly than usual, there was lots of squeaking, and I got nervous so I took cheerio out. They play together on neutral territory all the time & are very familiar with eachother. I would say that Daisy is the dominant one because she's older but she's only rough with Cheerio when she gets annoyed with her, it's like shes showing cheerio what's okay and not okay.
I want to know if there's anything to do to make the move-In more friendly & safe. I've read that putting vanilla extract on their rumps & thoroughly cleaning the cage before putting them back in it, but is there anything else that would help in the beginning?
I'm worried that they won't be able to live together because They don't get along

Have you done intros with them? They are together during the day or play time? You definitely need to scrub down the cage before moving in any new rats into the cage. But the louder squabble at night is pretty normal. If nobody gets cut up or Cheerio doesn't get extremely scared of Daisy, then it should be ok to leave them together.

this info might help http://www.ratshackforum.com/forum/showthread.php?t=32368

I agree with Jo, I hear most of my squabbles at night. Also, if there is no blood or wounds and the majority of the time they get along and sleep together, etc, then they're probably just fine. Most likely working out their pecking order or someone is a rough groomer. Maybe a bit of both at the same time.
I currently have 6 boys living together in my DCN (different ages and litters) and they squabble and box and sometimes chase each other around (it's almost always involving this 1 particular naughty boy) but they never hurt one another, they cuddle and sleep together, groom each other, and still get along great.
Good luck and don't let the small squabbles deter you. If there is no harm being done then you may have a girl who squeals when she doesn't need to! haha

Intros of all animals will first be suspicious, and often territorial. I had problems with all cats, and rats, and even some with dogs. They get over it after squabbling for a while. They will choose a corner, and take a time out.