You have not been dealt a very good hand with this situation. I am not that familiar with all that you have been through, but have you considered getting in touch with another doctor and seeing if there is some other course of treatment besides what the oncologist suggests?

As far as your in-laws you can keep them informed. However, with the situation being as serious as it is you shouldn't have to deal with their crap. Tell them they are welcome if they are there to support their son and you during his illness. If all they want to do is cause strife tell them to stay away. Who needs their junk on top of all the other stuff you have to deal with.

My thoughts and prayers are with you.