How can i do more then 5 returns ( grandchildren & myself) all of them are not e-filed and save on computer

The IRS imposes a limit of 5 e-mail returns.  Preparing greater than 5 returns is viewed by the IRS as being 'a preparer' and requires registration with the IRS.  It is NOT a TurboTax limitation, and it does not matter how many TurboTax packages you buy; if you try to e-file more than 5 returns you should consider it an invitation to the IRS to contact you.

NOTE: To prepare more than five e-files, you will need to become an Authorized e-file Provider and register as an ERO (Electronic Returns Originator) with the IRS, see:
http://www.irs.gov/Tax-Professionals/e-File-Providers-&-Partners/Become-an-Authorized-e-file-Provider
    Intuit has 2 products for tax preparers:
      ProSeries    http://proseries.intuit.com/
      Lacerte    http://lacerte.intuit.com/index.jsp

However; while you can only e-file 5 returns, the TurboTax software will let you PRINT and MAIL as many additional copies as you need at NO additional charge for the federal returns.

Can I still prepare additional tax returns as self-prepared by the client using the same copy of the software or should I buy separate copy 

What do you mean "by the client?"    If you are  a paid tax preparer you are in violation of the terms of service if you are using TurboTax to prepare returns for people who are paying you.  If you have the credentials to be a paid preparer you need to use the professional tax software.

https://proconnect.intuit.com/?s_cid=TT.com_MoreProds-Footer_ProTaxSoftware