Can Family members access the files stored on other users' accounts? Do we need extra disk space?

Thanks for posting your questions on our Community, tarun3agarwal5!

When upgrading to a Family plan, each member will basically have their own Dropbox account and they can choose what to share with the rest of the members. In other words, the rest of the members won’t be able to see other members' files, unless they’ve been manually shared with them. Feel free to check out more info here.

The only exception is the Family Room folder that’s automatically created for all Family members upon joining the plan. Whatever file/folder is added to that folder is automatically shared with everyone on the Family. 

As for your last question, the same rule applies for all Dropbox plans; if you sync files locally on the desktop app, you need to have enough hard drive space to accommodate them or else, you need to make them online-only/selectively sync them. This applies for the files you actually have stored on Dropbox and not for your overall Dropbox quota (which will be 2TB, if you upgrade to Family).

Hope this helps! I’m here for further questions though.