So based on your sig I'm guessing they'll be doing 2B next year? Hmm. Yes, I think your best bet is to have the oldest stay on the old schedule, if they're capable of doing the reading independently or you have the time to do that extra reading.
Claire - Tasmanian mum sharing one of God's garden beds with four other 'Son-flowers' - DH (husband of 22 years), Little Bear (DS 18yo, AO Year 11/12 - his LAST YEAR!!), Miss Muffet (DD 16 yo, AO Year 11) and Mouse (DS 13yo, AO Year 7 - 3 teenagers, yikes!).
"A child of any age should be a well-read person for his age." - Charlotte Mason
"A child of any age should be a well-read person for his age." - Charlotte Mason