yes, it is a terrible idea... there are so many things that can go wrong...
the biggest issue is that the Bredli needs it much hotter than the GTP does plus the humidity/daily misting for the GTP really isn't great for the bredli.
then there is stress on both parties, one could eat the other, they would compete for the best spots (bredli are semi arboreal so they do climb if perches are available), size difference, etc... the list goes on and on