Its really not advisable. It wouldn't be the worst mix I've heard of, but the issues of hybridization and cross contamination of diseases is still an issue.
My T. verrucosus have shown no interest in leaving the water at all, whereas Kweichows will live on land for extended periods, so you would be compromising their their needs by keeping the in the same tank. It would be much better to have a separate enclosure for both species that provides optimal conditions for each.
The bottom line is to mix any species has numerous risks attached for the animals involved and absolutely no benefits, even for species that have broadly similar requirements.