Well, I am not familar with Edge 530, so there may be perhaps a better solution, if the device supports multi-user profiles, but for that you better ask on the forum dedicated to the device, instead of here on the GC Web forum.

The only solution I see for sharing the same device among multiple users, is using a general GC account for the device alone (master account) , and then a separate GC account for every member of the family. You'll be syncing the device to the master account, which will keep the activities of all the family, and export them all as FIT files (Activity page cogwheel menu » Export Original), and importing them then into the account of the respective user to whom they belong (on the Import page).

The disatvantage of such sharing is, of course, that you'll not have any usable VO₂Max or Training Effect data or stats, because the data will be mixed up from all users. Some other functions, like Personal Records, life totals, etc. may be also negatively influenced.