I'd want a culture done for sure...and NOT another round of "more of the same". Totally agree on not feeding during treatment, or feed very lightly if you feel
you must give something. Heavy meals should be avoided...many snakes won't even eat, they don't feel that well. Yours might regurge this, don't be shocked.
No way we can tell you what the risk to your other snakes is at this point...but a culture should help with that. Good luck! One sick snake is bad enough.
BTW, how long have you had Mars?