What should I do?

I owned a critical area for severial years, the busiess growth recently, company hired a new engineer title is higher than me. Manager like the new huy as team lead, his english and mangement skill is strong, took the credit as tech lead, I need solve many critical issues in his project. And the manger and the new guy want more people get familar with my area, I fell my position is not critical in a long run, how to protect my self? Manager and the new guy keep assign new people in my area and I need tell them how to do it, I feel no future. Any suggestion?