Even 'em are here! How can I do this? と Even 'em are there ! How can I do this? と Even they are there! How can I do this? はどう違いますか？説明が難しい場合は、例文を教えて下さい。

The first two examples don’t sound natural. “‘Em” is very informal and generally used only in spoken language. It’s the contraction of “them”. The most natural is “Even they are there! How can I do this?” But I would change it a bit like this: “They are even there! How can I do this?”