The question should be, 'Are the following sentences correct?'
All of your sentences are possible.
The subjunctive in, 'If your grandma were alive, she would be happy to see that you have a family now' is more common in AmE than in BrE where you would often find 'was', but different people use it differently.
As for, 'If you studied Chinese, you would realize that it was/is not as hard as you think/thought' almost any combination could be used. I would probably use 'is' and 'think' but it's a question of preference and of what you want to stress.
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