Port 80/443 router conflict

[Carlton Brooks]

I have a successful homeassistant setup running on a NUC with a 
letsencrypt certificate. It uses Port 80 and 443 for internet access.

I just bought a Synology NAS disk station DS918+ to do all my bacups etc.

If I want to access the outside world with the NAS with an SSL or 
Letsencrypt certificate, I again need to have port 80/443 open.

This is where I need help. I will admit the lack of knowledge at this 
point but I do know that two devices can not share the same ports, but 
how might I configure the NAS to gain outside secure access.

I can get a domain name but am confused as to using a DDNS or cname to 
gain access.

Any help in "somewhat" simple terms would be greatly appreciated.

Thanks

Carlton Brooks