Hi and welcome to the world of 'Malawi' Cichlids
Your tank sounds just about ok for the two species that you wish to have in it
Both the two species you have picked tend to be of the less aggressive ones and also as a direct result for these two species only it is not CRITICAL that you get the M/F ratio spot on, ie you can have more than one male in the tank of each species
That said you should always try and have more females than males, it's just a question of how many...
I would say that a group of 6 Acei 2M/4F would work well with a group of 8 yellow labs say 2/6 or 3/5 worst case 4/4 and see how it goes from there..
The trouble is the males and females are hard to sex accurately in both these species particulalry in juve fish of less than 2" and above that size can still be hit and miss except for the dominant male of each species... the key is to understanding the differences between sub-dom males and females

which is harder said than done
what are the water stats like in your part of the world, you ideally need high pH and hard water for Malawis to work well in??
Hopefully this has helped you a bit
Regards,
Dru.