Is Amharic mutually intelligible with Oromo and/or Tigrinia?
With Oromo, no. Oromo is from a different language group altogether. There are some cognates that Amharic and Tigriña share, but they are about as mutually intelligible as English and French. The closest two Ethiopic languages are Tigriña and Tigre and this pair probably has the most inter-intelligibility. Hariri (Aderiña) and Guragiña are also somewhat close.