The astronaut figures supplied with Spacex toys have a number of different origins. Initially, they're all derived from other toy figures. And most also show details that are clearly based on real-life pressure suit designs.
Eight figures appear to be original designs by LP, which had previously been available in various sets of space toys produced by that company.
As a note, I've sometimes seen Spacex figures described as being copies of Marx designs (even apart from word-spamming on eBay). I don't know much about Marx toys, but have seen more than enough of their figures over the years to know this isn't the case. There are Marx spacemen that come close to some MPC figures in general impression, but so far I haven't seen any Marx figures identical - especially in pose - to any of the Spacex figures.