Networking PC and Macs Plus Backup Issues

[wallyclan]

Need help getting my three Macs and my three PC to talk to each other but also back up to one of my external drives. I have a 4 TB Seagate with Ex Fat and also an 8 TB Apollo My Cloud and also an old WD 2 TB drive that I have been using because WD provided easy software to see all the drives and you can select which files you wanted to backup. That drive is no longer being supported. The Apollo drive is somewhat cumbersome for me to select which "user" is which because each one requires it's own password. With the WD software you could have separate "folders" for each user - all in what they call the Public Files. I'm afraid to reformat the Apollo drive since I'm not sure what to do. I need advice on which drive to use and what software would give me the ability to read and write to and from any of my computers. It's overwhelming to me