Ok Custie, am I right in thinking that the two existing pendants are switched on together ?
If so the pendant nearest the switch will probably have 3 cables, a feed in, a switch wire and a switched live & neutral to the far pendant. I'd replace the switch wire with a 3 core and CPC giving two switched returns and install a MF junction box above where the pendant with 3 cables is now. Then just run a new T&E from there to each bank of lights looping in and out, the s/l and neutral to the end of circuit light can be replaced or used to feed the first downlight on one of your 2 banks.