hey there, the zinc level is not as terrible as some, but he could try to get it up closer to 18 umol/L which for you would be 1.20 ug/mL
the magnesium level of 2.3 looks okay. when i convert it over it's 0.94. he has to ensure he goes no lower than 0.90 mmol/L (2.2 mg/dL) so he can still go higher than his current level. i think you would be fine to keep the d3 to 4 times a week, and take the mineral combo as you say until you run out and can find separate components.
bahaha world without zinc https://www.youtube.com/watch?v=U1iCZpFMYd0