It’s the “wolf-goat-cabbage” problem. Simples.
(1) Build very large orbital station on high polar orbit: this is Ground Zero.
(2) On it, build IPS1 (interplanetary space one) which is the large Mars-orbital station. This will leave for Mars and never return.
(3) While IPS1 is with us, build the required Mars-landing/exiting daughter-craft plus the main large return-pod for the first returnees to Earth from Mars Ground Zero via a stopoff on the way back on IpS1 in Mars orbit.
(4) Launch IPS1 plus all its daughter-craft, listed in (3), target Mars, containing all necessary materials for seeting up the first ground colony/colonies, first probably of pioneer scientists and engineers.
(5) On Ground Zero build smaller planetary-crossing craft to act as subsequent shuttles, probably like the return-pods. If they can come back, they can go out too. Ferry further supplies and personnel as needed.
(6) Build IPS2 on Ground Zero, a copy of IPS1 incorporating mods found necessray from IPS1, and send it out, with more shuttles and supplies. It too does not need to return ever.