Yeah I think they like groups of a few more so I`m going to keep an eye out for some, they are about 5cm, one being slightly bigger haven`t a clue how to tell which is male and female. (female the larger one?)
Don't quote me on this but I believe you have to physically inspect them (if you get my meaning) unless I imagined that. Found this snippet so I was right:
Sexing: When trying to sex your synodontis, first you'll need to catch it.... Good Luck...

Next pull the tail down gently, doing this should straighten the pelvic fins to reveal a furrow tissue underneath. The furrow will open to display the anus of the fish and the genital pore.The female will show an extended papillea but the oviduct is on the ventral side of ths papillea; if the female is mature a slight redness might be apparant. A small or thin female may have 2 pink pores, oviduct and anus. Males on the other hand have quite a ridged genital papillae on which the spermatoduct is on the back end facing towards the tail fin.
Females may apear more 'plump' also.