The biggest obstacle to having anyone steal your idea is sheer laziness. For cofounders, it'll be worse than that – they already know roughly how much work is involved, and already have a team of dedicated souls to execute it. The worst possible mistake at this point would be to try and replicate all that on their own, or with a new team (who would, perhaps, also know on some level that they're working with/for someone willing to steal another's ideas, bad scene…)
Practically speaking, it's much more likely that your team will hang together through product launch, and then have a falling out over a funding round issue, exit offer, or disagreement over how long to hang in without revenue before trying a pivot.
In the meantime, get your nose back on the grindstone, build whatever it is, and launch the damn thing.