I adopted two brothers, Siamese cats...they're 6 and very bossy bright.
They are litter trained and although they go outside to play, they will not go in their tray when I put it in the garden. They both pee'd and poo'd on my bed.
Bless them.. 
This was about 5 weeks ago...I had only had them for 3 weeks and it may have been too soon....shall I try again?
Is there some trick to it?