With a rank of 43,000 in the NEET PG under the OBC reservation category, securing a seat for a Diploma in National Board (DNB) in Family Medicine may be challenging, but it's not entirely out of reach, especially under state quotas or in less competitive institutions.

DNB programs tend to have higher cutoffs due to the limited number of seats and the program's popularity. However, the exact cutoff for each specialty and institution varies annually based on factors like the number of applicants, available seats, and the specific state's reservation policies.

Your best chances may be in less sought-after institutions or by exploring state-level counseling options, where cutoffs can be lower than in all-India counseling. Additionally, some private institutions might have seats available, although these may come with higher tuition fees.

It's advisable to participate in all rounds of counseling and explore state-specific quotas and private institutions. Consulting the latest counseling results and speaking directly with the institutions may provide more clarity on your son's chances.