Actually not a huge amount! I already had the older pair and the only research I had been doing was on breeding robos. Then I rescued the young pair. A couple of months later one of the older pair, Cookie, developed a tumour and so because I worried about how her sister would cope living alone after she passed I decided to move the two pairs in with each other. I just did it slowly and carefully in an empty, clean cage, added more toys over the days and they just took to it really well!
This was them on their first night together <3