Well I've now added another litter tray (they only had one left in the petshop so will get another one this week from a different shop) and put it behind the toilet. I couldn't fit it in the exact same place they have been going to the toilet but its less than a foot away and they still pooped on the floor and not the tray! I did pick it up and put it in the litter tray though and since then we've not had any other accidents and I've seen both of them using the other tray downstairs but neither of them have used the new tray.
On the dominant issue though I've been observing their behaviour very closely this weekend and Zoot the male is definitely more dominant than Lexi the female. If they are eating then he will push her out of the way and eat out of her bowl and she just stands there looking at him and after a while starts to eat out of his bowl. I then fed them at opposite ends of the kitchen but Zoot still went over and pushed Lexi out of the way.
The same goes with toys, if she's got something he wants then she'll just give it to him straight away, the same goes with treats. They were also playing on Saturday and it got slightly out of hand and they were both making a racket and hissing at each other. When I intervened I found Lexi's hair stuck to Zoot's paws.
Is this normal behaviour for two cats or is there something that I can do to help the situation, I feel awful for poor Lexi.
I must add though that they aren't always like this, at the moment they are both laying next to me fast asleep.