Take heart Marge, they caught the leukemia much earlier than they would have otherwise so the treatment there is coming earlier too. Good news there. The shingles are likely what is giving him so much pain. My Dad went through shingles and chemo treatments at the same time in his 70's and it was so hard to see him struggle like that. He came through it though. John is young and strong and you have a wonderful support system. I know its so scary and hard coming so soon after Paul, and my heart is aching for you sweet lady. You have my prayers and a shoulder and hug whenever you want them.
PS. Not sure what is available to you there, but my Dad visited a highly acclaimed acupuncturist who relieved so much of the shingles pain he was able to get out of bed and start LIVING again. A thought for John. Sometimes acupuncture can help with the nausea too.
Big hugs Marge, I know this is a horrible time for your family. We are with you.