Who is responsible for liens/mortgages left on property bought at a tax sale?

In most states they are wiped out. That is why most mortgage companies either escrow for taxes or subscribe to a tax service to notify them if taxes aren't paid. Most States are careful to notify the mortgage lender as well.

2. Is it possible to wholesale properties bought at tax sale during the one-year redemption period?

It is, but you would need to disclose that the sale is "subject to" the right of redemption. Far better deal is to go buy the right of redemption from the lender, get the deed from the owner and you have closed the loop!