Here's some more ideas. All these options are fine: He was not [who / what / how / like / as / the way] he seemed to be. Note: there is a risk of offending someone by speaking like this. Because it's like calling someone "two faced" and "fake". So it's important to elaborate, giving more detail, to make clear you're not calling him "fake" or "two faced". For example: "Initially I thought he would be like this, but once I got to know him I realised he was like that." - This way you're admitting you made a mistake of pre-judging him, rather than him making a mistake of being fake. A comma is not strictly needed in these sentences, but helps a lot in making them easier to understand instantly: Those whom the angels love most, tend to die young. Whoever god loves, seems to die young. Note: saying "gods" is blasphemous (sinful, and sometimes offensive) to Christians and Muslims because they are monotheistic (they do not believe in multiple gods, and they often believe it's a big sin to suggest there are multiple gods). So I recommend using the singular "god" and/or multiple "angels".

The only strictly wrong ones are 1c and 1d. While not strictly wrong, 2f & 2g are very inefficiently worded. Some people would say they're wrong, but I won't. All the rest are OK, but most have room for improvement.

Because there are multiple ways to express the same meaning，I should try to choose the method by which I can express my information in the correct form. It is very likely not the best method but as long as I can express it correctly, any method is fine. Even if what I write is very awkward or verbose, in my opinion, as long as the meaning is correct, it is correct. After all, I am Chinese and not a native English speaker, so my English proficiency is very limited. So my requirement for understanding and writing sentences is not high. As long as there is no ambiguity or different interpretations in my language or sentences, it's fine, which is the minimum standard. So I don't pursue the best writing style. This is the minimum standard for beginners learning English. When the level is improved in the future, then more perfect sentences can be written.

Here are the grammatically correct sentences: 1. 1a. He was not who he seemed to be. 1b. He was not the man that he seemed to be. 2. 2c. Those whom the gods love die young. 2d. Those who the gods love die when they are young. 2e. Those who the gods love die when young. 2g. Those who, when young, the gods love die. The rest are either ungrammatical or sound awkward.