You can answer personal questions if you want to. Opening up to patients can help them open up to you. It's up to you to draw your own boundaries. But most patients will respect a boundary once you've made it clear (except manic patients, but they're not paying much attention to your answers anyway).

Splitting is more difficult, and you'll come across it a lot. The best thing to do is to explore the patient's attitudes without giving anything away yourself. Ask them plenty of questions about what the staff member has done, why they think it's wrong, how they think the staff member could change their approach etc. You see splitting with personality disorder patients and they usually love to talk. Keeps you on side without taking sides plus you might get some useful information as well.