I got their reply on twitter:

You will be able to check in at the airport. My colleagues will assign you a seat for free

As to whether or not a check in fee will be added the answer is no. OP states the following in the comments:

with eurowings you can check-in in person at no cost. The online process just speeds it up,

I got their reply on twitter:

You will be able to check in at the airport. My colleagues will assign you a seat for free

As to whether or not a check in fee will be added the answer is no: with eurowings you can check in in person at no cost. The online process just speeds it up, allowing you to skip the queue when you have no stored luggage, and lets you choose the seat earlier

I got their reply on twitter:

You will be able to check in at the airport. My colleagues will assign you a seat for free

I got their reply on twitter:

You will be able to check in at the airport. My colleagues will assign you a seat for free

As to whether or not a check in fee will be added the answer is no. OP states the following in the comments:

with eurowings you can check-in in person at no cost. The online process just speeds it up,