Our rental agreement includes a husband and wife. The husband has behavioural problems, and I know I can serve an N5 but is it possible to evict only the husband and leave the wife only as the tenant?

It is not possible to evict only the husband. Both the husband and wife are listed as tenants on the same lease, they are considered co-tenants, and the tenancy is treated as one agreement. This means you cannot evict just one tenant using a Form N5 while allowing the other to remain. Any notice of termination would apply to the entire tenancy, not just one individual.
If the behaviour is serious, you may still serve an N5 based on the husband’s conduct, but it would be against all tenants named on the lease.