If growth plates are fused in a 16 year old male, does that mean that any further growth of penis and testicles are also halted? or do those organs grow until you are 18?

Neither.: There is little relationship between the end of bone growth and the end of sexual development. A young man whose growth plates of his bones are fused may have already stopped genital development, or may see continued maturation. 18 is not a magic age where everything stops changing; adolescent changes in the genitals may stop well before age 18 or, in some young men, continue til the early 20s.