1). As far as I know that Microsoft actually does not provide us one tool to migrate code from SVN to TFS2008. However, you can achieve that by using Kyrosoft SVN-2-TFS2008. See:
2). Yes, it is possible for you to migrate code from TFS2010 to TFS2008. You should use the TFS Integration Platform to do the work for you. See:
And for your scenario, I personally recommend you to first migrate code from SVN to TFS2010 and then migrate from TFS2010 to TFS2008.