Re: can pregnant women be around chemotherapy patients?
Cancer's not contagious, so I can't imagine why it would be a concern. Both you and the cancer patient have a suppressed immune system, so just being around ANYONE can potentially cause problems because other people can introduce new germs to the patient or pregnant woman.
I'd be more worried about the stress of dealing with your MIL's illness at a time when you are more stressed anyway.
Best of luck to you and your family.