They might just need more time. I have a large, older pair of f1 Williamsi. Yes, a Mbuna that you can keep as a pair only. My Male is 5" & female is 4" spawned numerous times. I have never known them to be skitish or their fry. Are they fry or adults? Granted my experience has only been this pair but, they have always been very out going.
I love them because they are very wild as fry but, very mellow in comparison to other Mbuna as adults. Also a very uncommon Mbuna.