Nothern Kyushu JR Pass to Mojiko/Yahata

I've bought the 5-day Northern Kyushu JR Pass with plans to travel from Hakata to Mojiko, Mojiko-Yahata, Yahata-Hakata on the same day. My searches on Hyperdia came up as below:

9.38am-10.43am - Hakata-Mojiko on the Ltd Express Kirameki line
2.07pm-2.37pm - Mojiko-Yahata on the JR Kagoshima Line Section for Futsukaichi
6.23pm-7.22pm - Yahata-Hakata on the JR Kagoshima Line Rapid for HAINUZUKA

My questions:
1. I just want to check if the JR Pass can be used for these trains - especially for the Kagoshima line as there is little clarity if those can be used for the Northern Kyushu JR Pass.
2. Is there a need to reserve seats for these trains in advance?

Kagoshima line to Kumamoto is inside the validity zone

Thanks so much!
We are arriving the day before where we will exchange our voucher for the JR Pass in Hakata station. Just to confirm that we should have enough time for us to book our seats for these trains? I'm not sure how popular these trains are and if there will be packed to the brim.

Well two are just regular commuter services. No booking seats.

The Kirameki I don't think has reserved seating. But you can always ask. I would've assumed it did, but the JR Kyushu website doesn't highlight the fact.

Got it. Appreciate all your help.