We are developing our Education based interactive teaching LMS system and we have developed two logins for that in PHP (YII). However, now we are working on two more logins and these logins will control the features of previous two logins. The issue we are facing is that we started these current developments in YII and we have to make changes now and then as per requirement. Someone suggested us that instead of YII we should develop these two logins in CORE PHP instead of YII. Now our doubts are:

1. Will there be any issue if we use CORE PHP now for these two logins instead of YII. So can we go with Core PHP or the only option is YII. We can start development for these two logins from scratch.
2. If we select CORE PHP for this and further development will this affect the working, functionality, scalability or quality of my LMS.
3. Will there be any security issues if we go with core PHP and which one is better considering security.
4. As we have to make changes now and then while development , which one is better considering changes : CORE PHP or YII

Please suggest so that we can proceed further.