401k to Roth IRA

My husband is self employed this year and starting up his own business. However, he has two 401k accounts from two previous employers. One has $1,700 and the other $16,000. I know if we convert we will have to pay taxes, probably around $3,000 to $4,000. Question would be do we convert it or leave it as is and start a separate Roth IRA? And if we converted, when do the taxes have to be paid (immediately or when taxes are filed?). It looks like the dollar amount continues to decrease on his 401k from Fidelity fees but I’m not sure if it’s just that or just what the $ are invested in. Advice? Thank you!!

Hi Wendie,
May I ask why you are considering transferring it to a Roth IRA instead of a traditional IRA?