If I received 2 Forms 1099-R from the same institution, same dates, different amounts, which one should i use to file? The one with the least or bigger amounts?

Is one a corrected 1099-R that replaces the first one?      Ask the financial institution why you received two.

And...the codes in box 7?

If you've been getting monthly payments, then in the year you turn 59.5 years old, you do get two 1099-R forms.

One for the before age 59.5 (usually box 7 is code 2)

...and another for the after age 59.5 payments (usually the box 7 code is a 7)