Does it mean we have to do soft fork every 28 days? It is very inconvenient for the miners. Hope they will find a better solution.
No, they only ne4ed to soft-fork once. The soft fork will permanently freeze any Ether in The DAO and all of its clones (children.)
Does it apply to the hacked the DAO only or to the "rescued" DAO as well? If later, they will another fight to get it back.
It applies to the hacked DAO and all its clones. That's why the folks involved are pushing hard for a hard fork that would replace all DAO instances of code with simple withdrawal contracts. If that hard fork goes through, all of them will be emptied and the ETH recovered.