Hi Stephannie! I'm so excited for you to begin, and it sounds like you are getting all of your ducks in a row.

I can't remember which guide you are going to be using? Each of the extension packs has content that is meant for the more mature reader, so you'd have to weigh whether the titles would be appropriate for your 8 yo to hear. I looked at the PHFHG extension last year to possibly read out loud to my 8 yo or have him read the titles independently in his free time, and I decided not to do that. PHFHG is a very history rich program without the extensions, the extension books are at a mid-fifth to upper-seventh grade reading level, and toward the middle to the end of the extension pack, there are quite a few pages being read each day - which would be perfect for an older child reading them independently, but not so perfect for mom reading them all out loud.

However, I have 3 very different aged dc with very different needs, and I'm not at the point where I enjoy reading extra books out loud for long periods of time. If you would enjoy that, and you feel the books are appropriate in content for your 8 yo, then it would probably be fine.

I would think the CTC extension package would not be appropriate to be read out loud to a younger child due to the mature content of the time period being studied, if that is the guide you might be using. Bigger Hearts would probably be fine.
In the Appendix of the guides, right before the Extension Package Schedule, you'll see the rotation of response activities the older dc should do for the extension pack. It is important to have your older child do these, as they are also what extend the learning. They are usually things like oral narrations, several paragraphs long summaries, draw a picture with a summary, etc. - and they are somewhat different depending on which guide you are using.
The reading of the extensions independently is one of the ways the program is beefed up for your older child, but you could decide if you think it's alright to read them yourself instead. I think if I were you, I'd start out not reading them out loud and do the plans for about a month to see if you'd enjoy adding that to your plate, as well as seeing if you thought your older ds needed the benefit of extending the history by him doing the reading independently. Then, you could always start reading it out loud to your 2 kiddos at that point if you still wanted to - I have a feeling once you'd begin doing the reading yourself, you wouldn't be able to go back and make it independent as easily if you wanted to.

Those are just my thoughts though - you will truly know best!
In Christ,
Julie