Backyard Danger: Family's Shocking Structural Hazard Sparks Safety Alarm

Dear Abby: My brother-in-law recently built a deck in his backyard, and I'm deeply worried about its safety. While he's proud of his DIY project, I've noticed some serious structural concerns that could potentially lead to dangerous accidents.
The deck appears unstable and lacks proper construction techniques. I'm genuinely afraid that someone—perhaps a child, elderly relative, or unsuspecting guest—could be seriously injured if they were to step on it. My concerns stem from visible signs of poor craftsmanship, including wobbly railings and uneven surface areas.
I want to approach this sensitively without embarrassing my brother-in-law or damaging our family relationship. How can I express my safety concerns without coming across as critical or undermining his pride in his handiwork? I believe professional intervention or at least a professional inspection might be necessary to prevent a potential tragedy.
What steps would you recommend I take to address this delicate situation while prioritizing the safety of my family members?