The project Y requires the Object Repository of project X — this implies these two should not be separated. I would rather recommend you to merge the project X and Y to form one project for easier maintenance over time.
You can make sub folders in Test Cases/Object Repository/Test Suites. You can create sub-folders named X and Y in a project. The test cases under the sub-folder Y can use all the Test Objects under the sub-folder X. It’s simple. No need to worry about how to share a Object Repository across multiple projects.
Do you want to assign the project X to Mr.X and the project Y to Ms.Y? so you want to separate the two? — You shouldn’t. Mr.X and Ms.Y should share the single/united project using Git. See the following post for my opinion.