In the first case, you already know this foreign invention patent, which means that this foreign invention patent has been published. At this time, copying to China does not meet the requirements of novelty. You can apply (no one can stop you from applying), but you can't be granted a patent;
In the second case, the improvement based on it is at least novel, depending on whether the improvement is obvious. For example, somebody else's patent defines four screws, and you improve it to eight. This improvement is not creative, but it is still not patentable, but if it is not obvious, it meets the requirements of creativity and can be patented;
In the third case, there is no problem at all. If you dare to quote, we recommend it.
If you don't understand, hey me.