There definetly will not be a territorial problem,not with siblings,no matter how small your place is.
I honestly do not think anybody should have just one cat and if you can get siblings,that's just great.
They will not ever be lonely,will always have each other and you'll have a great time watching them play and interact with each other.
There is a poor little girl-kitty a couple of houses from me,she sits in the window looking out,all the time,beeing alone a lot.
To add to that,she's also been declawed
She has a home which is great,but I still look at her sweet little face in the window and I feel sorry for her..