What to put with Convicts or RTS - do they mix?

Hi All,
I'm posting this on behalf of a friend....

She is just about to get a 30 gall (UK) tank and is taken with the idea of
getting some Convicts....She also has a Red Tail Shark that really, really
needs moving from a smaller tank. She has asked me for advice on stocking
(plus environment which I think I can handle at the moment but may post in
future).

Do you think the Convicts would mix with the RTS? Or should I be going for
steering her away from the Convicts - afterall they already have the RTS
that needs the move?

Thanks
Gill