Network – My sites are unavailable

You have site1 and site2 folders on your server, so Apache is serving those hence the file listing. Multisite however is trying to serve those sites using URL rewriting, so deleting those folders should fix the issue

Multisite Tables the same as Single Install?

There’re some special tables Codex Link in Multisite. In short: No you can’t. But you can degrade to a single site install and then import them there. If in doubt, simply add a new local multisite install, import the posts there, downgrade to single site and then export/import again.