Two force members

A $2F$ member requires forces $($no moments$)$ acting at exactly two points in the FBD of the member. $BD$ and CE are therefore the two force members in the structure

Useful FBD

There are no useful equilibrium equations for $2$ F member $(BD$ and $CE$ in this problem$).$

Hence the FBD with useful equilibrium equations is meber ABC

Using the FBD$/$equilibrium equations for member ABC,

$($a$)$ the magnitude of the internal reaction force for member BD is $(kN)$ and the member is in

$($b$)$ the magnitude of the internal reaction force for member CE is $(kN)$ and the member is in