Just A Couple Of Questions

I am curious about a couple of things. I understand that a 1st, 2nd, or 3rd can be foreclosed on in any order. The first to file in court will normally have primacy. My questions: 1. If a senior mortgage or lein forecloses, does a junior position have the right to bring the senior instrument current and assume the debt? 2. Do foreclosures of mortgages and deeds of trust have the same rights? 3.. If I accquired a discounted 2nd or 3rd, does the bank or holder of the 1st have any legal obligation to allow me to bring a forclosure of the 1st current? I would be grateful for any enlightment. Thank you