DNS help before I go insane . . . .

I have searched and found about every DNS entry help except the one I need.

On the WHM server, I want to have a DNS entry as follows:
- the DNS is managed by us
- the mail mx goes to us, as does mail.domain.com
- web www access goes to a web hosting site somewhere at a third party where the web site lives
- access without the www (domain.com) also goes to the website elsewhere
- ftp goes to website server as well
- cpanel, webmail (www.domain.com/webmail) comes to us even though website does not
- assume we cannot access the server where the website is, so we cannot move it to us or change it in any way.

TIA