I would guess they would need to monitor his blood calcium levels closely, to ensure it doesn't get too high. Some bone mets leach calcium out of the bones, and that combined with taking extra calcium could cause hypercalcemia (symptoms include nausea and temporary dementia). I think many people with bone mets do continue on calcium OK, but it should be monitored.
They might want to put him on a bisphosphonate or Denomusab in addition or instead of calcium.
So definitely a question for his medical team.