SIbling Cats and a Move

I'd appreciate feedback and thoughts on this situation...

I have two adult cats (roughly 4 years old) who have grown up exclusively with each other in the same house together since they were wee kittens. The two sisters normally sleep, play, and groom together in a very close relationship.  Two days ago I moved the two of them into my girlfriend's house as we are consolidating our homes together.  She has two permanent adult cats and three rescue foster cats (a 6 month old and two 5 week olds).  

I've put the two siblings (sisters) in a separate, closed bedroom with their original litter box and regular food before we let them out to the rest of the house and cats.  They've been slowly relaxing.  However, they've had an odd and concerning behaviour of hissing and baring their teeth at each other every time they see their sibling in the bedroom.  I'm not sure why they are scared or threatened by each other. 

Is this common?  Any thoughts to help alleviate the situation?

Thanks in advance!
Greg.

Hi, and welcome to TCS

It's most likely redirected aggression. They're aware of and unsettled by your GF's cats, but can't get to or away from them, so take it out on each other slightly. It is concerning, and you definitely don't want it to escalate. As it's so mild at this stage, I suggest you take a cloth for each of them and rub them all over (like for scent swapping). Afterwards, add a touch of vanilla to each cloth, swap the cloths over (so they each get their sister's cloth this time) and rub them down again. This way, they will both smell the same, and it will hopefully help them to relax around each other. I'd also suggest that adding a second litterbox for the sisters as it may help ease tensions a little. Don't forget the importance of interactive playtime too.

Remember this is a huge change for them, so allow them plenty of time to get comfortable before starting really gradual introductions. Always let the cats dictate the pace.

Feliway can be an enormous help at time like this, and Spirit Essences and Composure are always worth bearing in mind.

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