Retrieving intermediate table specific columns

The first problem will be solved by creating many to many relationships.

In your User model:

public function courses()
{
    return $this->belongsToMany(Course::class);
}
public function statuses()
{
    return $this->hasMany(Status::class);
}

In your Course model:

public function users()
{
    return $this->belongsToMany(User::class);
}
public function statuses()
{
    return $this->hasMany(Status::class);
}

You must create a table for the many to many relationships, you can see an example at official Laravel documentation: https://laravel.com/docs/5.7/eloquent-relationships#many-to-many.

After that, you can check user's course like that:

if($user->courses()->find($course_id)){
    //check IsStatus
    if($user->statuses()->find($course_id)->IsStatus){
    //some actions
    }
}

The second problem will also be solved by creating relationships between instructor and other models.

You are using many-to-many relationship between course table and user table. On you relationship you should specify which columns

...
public function courses()
{
    return $this->belongsToMany(Course::class)->withPivot('column1', 'column2');
}

than,

$user = App\User::find(1);

foreach ($user->courses as $role) {
    echo $role->pivot->column1;
}

https://laravel.com/docs/5.7/eloquent-relationships#many-to-many

My user Model.

public function courses(){
        return $this->hasMany(Course::class);
    }

public function students()
    {
        return $this->hasManyThrough(User::class,Course_user::class,'user_id','user_id','id');
    }

There is a User Model

There is a Course Model

There is a course_user , which is an Intermediate table.

What I need is to get

##Instructor->students