@Annie Sye hmm… ok so 2 things come to mind with him not tolerating capsules/pills. First, he may need gut lining support, and then possibly stomach acid support.
Please ask him to fill in this short Upper GI assessment form (from our Programs), and if he scores 4 or higher, consider trying the baking soda challenge (skip to the 3min mark) which is a non-diagnostic tool for seeing if there’s possible hypochlorhydria (suboptimal or low stomach acid).
If the above resonates with you and him, encourage him to support his gut lining for a period of time. He can do this with food therapy like 100-150mL raw organic cabbage juice daily for a month or two. Vary the color of cabbage (red has the strongest taste, white and napa cabbage are the easiest to begin with).
Now to answer your actual question…
Here are a few powder options with minimal inactive ingredients which he can try on their own or mixed with juice:
Thorne Magnesium Bisglycinate (already sweetened with monk fruit)
Seeking Health Magnesium Glycinate Powder (add to fresh OJ or infused water or smoothie since no sweetener added)
Chewable Options (with somewhat decent inactive ingredients). The majority of chewable options are magnesium citrate form which can be stimulating to the bowels, and potentially irritating to him as well in that form. This one is malate form:
Seeking Health Magnesium Malate Chewable