While it is always best and safer to discuss medical concerns with an MD vs an internet inquiry I will make a few personal observations. The COVID vaccines are new and thus do not have a long track record of possible impacts to draw upon.
Cancer drugs and treatments are not insignificant and can cause a number of issues. I have been there and at one point I needed to have my chemo treatments scaled back. On top of all of this you are also dealing with the potential of interactions between drugs and how they can impact a patient.
Radiation can also cause issues. When you add all of this up ... it can put a lot of stress on a patient and family. I would suggest you keep your MD's and nurses well informed as to what is going on. Speaking only from personal experience I would be VERY proactive when it comes to hydration. While all of this can be stressful on partners it sounds like you have some good communication going on between the two of you. Just take it one day at a time. Dennis(ProstateCancer.net TEAM)