@laulabell , have your parents got theirs visas? Hope your dad is ok.
We have very similar story except for paying everything as medicare doesnt cover for us. (non British)
My parents originally applied for 143 in May2016. They did health examination on 01/07/2020 follow by AoS. Unfortunately my dad was recently (Feb2021) diagnosed with exact same disease as your father. We are afraid that the medical will expire and he might need to redo the health check which may result in the worst for entire family.
We are keeping fingers crossed and hoping that their visas will come before the end of this FY.