will i get better hot water presssure from my new-ish combi boiler (30kw i think) if the cold main goes to the boiler first and then feeds all the cold taps after? at the mo when i run the cold tap the hot really slows down badly.

i think with high pressure systems the water goes to the cylinder first to balance the hot and cold, but i really not sure about whether the same applies to combis.

don't matter whats fed first your combi will only deliver probably around 10 l/min.
as for running two taps it will slow down it can only supply what your mains water supply delivers.
only way to get better flow is fit a larger mains supply pipe.