self-heating effect of dual PT100 temperature probe in a moving mass of water
You would be better off to get actual self-heating numbers from the probe manufacturer (or make measurements yourself). The coefficient can vary over a range of 10:1 depending on RTD element and probe construction (thin film vs. wound and epoxy vs. alumina packing, for example). The probe material will affect it too. TI is a semiconductor maker, not an expert in probe design. If you have a separate probe assembly loose inside a thermowell, it will be worse again! At least you have flowing water which is the next best thing to flowing molten metal. 

I would consider 5mA to be an excessive current for a Pt100, usually we use 1mA, so you are getting 25x as much self heating. That's a pretty heavy price to pay for a less professional design of signal conditioner if you care about accuracy. 

Most certainly the two elements will interact, again it will depend on the exact construction.