Hi,
Have you got the MAX31865 (PT100) modules, can you post a link to the data/spec sheet for the MODULES please.
The Micro can only supply a max current of 50mA.
Check the total module consumption, you may need to provide a separate 3.3V supply.
But first get your project going with one module.
If you bought a module, the supplier should also have sample code and library.
Tom... 