They surely had some cash, but I think it was a small contribution compared to Musk's. Given that Musk was $6.5M out of $7.5M series A, and something like $9-10M out of $13M series B, I think it's not possible they contributed more than Musk, unless they put big money into it right at the start (unlikely). I count find any concrete information about how much money the two actual founders contributed (which I consider as evidence that it wasn't much). Do you have some sources on how much they invested?