step 1: You have a current TN valid for at least 8 months. This is to make sure you get the EAD in time, since you cannot apply for another TN once you proceed to step 2..
step 2: You apply for I-140 & I-485 concurrently.
step 2a: You also apply for your EAD and your advance parole at the same time as step 2 above. Your spouse should do the same.
step 2b: Do not travel out of the country until you get step 3b below. You will need an advance parole document to get back in. You mention risk of failure. If there is any risk of failure its at step 2b. If you don't have a valid Advance Parole, you wil not get back into the US.
step 3: when you receive your EAD, you will notify your employer, and you tell them you've switched from TN to EAD. This invalidates your TN at this time. You can take the TN out of your passport now, since you have invalidated it. Your status is no longer "TN Status". Your status is now "I-485 adjustee status".
step 3a: Your spouse can work once they receive their EAD, unlike when they were on a TD.
step 3b: When you receive your Advance Parole you can travel. You show the CIS officer at the border your Advance Parole Document. If he asks if you have permission to work, you show him your EAD. Do not show him your TN, since you have invalidated it by using your EAD with your employer. Remember you are no longer in TN status. Your spouse must have their own copy of an Advance Parole.
note: Never apply for another TN Visa. Remember to renew your EAD every year and keep it valid until your I- 485 is approved.
This is completely legal. But it does not go without risk if the I-485 is denied.
step 2: You apply for I-140 & I-485 concurrently.
step 2a: You also apply for your EAD and your advance parole at the same time as step 2 above. Your spouse should do the same.
step 2b: Do not travel out of the country until you get step 3b below. You will need an advance parole document to get back in. You mention risk of failure. If there is any risk of failure its at step 2b. If you don't have a valid Advance Parole, you wil not get back into the US.
step 3: when you receive your EAD, you will notify your employer, and you tell them you've switched from TN to EAD. This invalidates your TN at this time. You can take the TN out of your passport now, since you have invalidated it. Your status is no longer "TN Status". Your status is now "I-485 adjustee status".
step 3a: Your spouse can work once they receive their EAD, unlike when they were on a TD.
step 3b: When you receive your Advance Parole you can travel. You show the CIS officer at the border your Advance Parole Document. If he asks if you have permission to work, you show him your EAD. Do not show him your TN, since you have invalidated it by using your EAD with your employer. Remember you are no longer in TN status. Your spouse must have their own copy of an Advance Parole.
note: Never apply for another TN Visa. Remember to renew your EAD every year and keep it valid until your I- 485 is approved.
This is completely legal. But it does not go without risk if the I-485 is denied.