Hi,
I am a Developer and VoIP, Telecom, and Linux expert from Pakistan. I have very good command on Asterisk, Twilio, and Voice and Video conferencing.
Regarding your requirement, I am afraid that video conferencing will not work with "dial-in" and "dial-out". cos normal phone (without a special video client/application) can't handle video calls. However this model can work perfectly for audio calls. Further I think only Twilio or Asterisk will suffice to full fill your requirements.
Please contact me to discuss project and let me know how you want to proceed.
Regards