1st time 2-man-questions

[chas]

Need some mechanics answers please:
1) R1 on 1st- on a steal and overthrow, who has play on R1 at 3rd?
2) R1 on 2nd or R1 on 2nd, R2 on 1st- on hit to F7 who has play at 3rd- PU or BU- I have been told both
3) R1 on 3rd, R2 on 2nd- on hit to F7 who has R2 at 3rd?
4) R1 on 2nd, R2 on 1st- on base hit who has R2 at 3rd?

Is there a simple formula to follow like BU has all first plays on the infield and then the trail runners. I thought that Bu had all 1st plays on the infield if the ball is hit on the infield. If the ball is hit to the outfield who has the first play at 3rd? Thanks.