"Pedro's Journal" is scheduled in the BHFHG Extensions, as well as in the Self-Study Deluxe package for the Newly Independent Reader" in PHFHG. If a student is doing the extensions in BHFHG, he will probably be doing the extensions in PHFHG, so that is not an overlap unless a student does both the PHFHG Self-Study Deluxe... and the Extensions.
Some moms do have their older dc do both though, as the activities in the Independent History Box coordinate with the Self-Study Deluxe books, and they are so neat they are hard to resist!
"Pedro's Journal" is scheduled from Unit 26, Day 4 through Unit 29, Day 2 of PHFHG's Independent History box. It is scheduled in Units 1 and 2 of Bigger Hearts Extensions plans. If you did choose to use it in both places, there would be almost 2 years in between the readings of it, and I know my ds has read it at least 4 times just for fun, so I guess I think it would be fine to use it twice, as the the follow-up skills learned along with it will be different and spaced out. Or, since it's the first extension book in Bigger Hearts, you could just skip it, giving your oldest time to get used to doing the daily plans of Bigger Hearts first, since this takes more time and teaching anyway.
As far as "Exploring Planet Earth", that title is used one time per week in Units 1-22; 32-34 in Bigger Hearts extension schedule. It has a rotation of follow-up skills that are more general in nature. "Exploring Planet Earth" is used in Option #1 of the daily plans of RTR from Unit 30, Day 3 through Unit 35. The daily science box plans are written specifically to correlate with this. Option #2 uses "Our Weather and Water" in place of "Exploring Planet Earth", and schedules that out in the RTR Appendix. So, several good options are available. If a student does "Exploring Planet Earth" within the Bigger Heart's extension, then the student could just do Option #2 with RTR. Or, since 3 years will have passed between doing BHFHG and RTR, the student could read it again within RTR otherwise, as the plans will be totally different with it anyway, and it is a good living book written in an engaging manner.
I just thought providing you with some details might better aid you in your decision here. HTH!
In Christ,
Julie