Next Payments and BOGO Credits Advice Needed

My wife, daughter, son, father-in-law, and mother-in-law are all on a family shared plan.  My son and father-in-law did a BOGO deal back in 2018 for iPhone 8s (I think my son's is the "free" one) and are about 21 payments in.  Unfortunately we took my son's iPhone 8 off the charger the other day and it was very, very hot and wouldn't turn on.  It continued to heat up until it finally cooled, but we have not been able to turn it on again (in fact, there is no evidence of any life in it).  We are considering what to do next (possibly try replacing the battery, but I suspect the internals may have been damaged by the excessive heat).  We currently have his sim card in an old iPhone 5 (which is struggling), but I am now concerned how that might impact the BOGO credits (since his iPhone 8 is no longer listed on the account, but instead the iPhone 5 is).  Will we no longer receive the BOGO credits if we can't get his iPhone 8 active with his sim card?  He is not eligible for an upgrade since we are still paying his phone off, and we can't trade it in when we reach the 80% paid point since his phone doesn't work at all.  One option we considered was using my mother-in-laws "upgrade" (she is the only one eligible) to get a iPhone SE, and then put my son's sim card into that for him and have my mother-in-law continue using her current iPhone 6 (with her sim card, obviously).  If we took that approach (and we kept paying off the broken iPhone 8), would we still receive the BOGO credits?

Any advice would be appreciated.