If you have cuda 9.1 installed and it works with TensorFlow, then it sounds like your card should at least support cuda 9.
But I assume you have tried
conda install pytorch torchvision -c pytorch
and it didn’t work?

Will there be a potential conflict between the versions, or they can coexist.
Regards

No, don’t worry, there won’t be a conflict if you don’t install PyTorch from source. If you use the pip or conda installer, PyTorch will come with it’s own separate cuda and cudnn bundle. This will be kept entirely separate and only used for PyTorch. This is by design to make the installation easier (this is also the reason why the pytorch binaries are so large). The only thing you may want to do is to update your graphics card driver to the latest version.