Eurostar tickets are to / from St Pancras only. Eurostar trains are currently not stopping at Ebbsfleet or Ashford.
If travelling by Eurostar, the transfer time on coach between Brussels and Cologne will be approximately 3.5hrs (including comfort stop).
Transfer times depend on your chosen airport:
For Cologne airport there is a 30 minute transfer to the ship (and vice versa).
For Dusseldorf airport there is a 50 minute transfer to the ship (and vice versa).
For Frankfurt airport there is an approximate 3 hour transfer to the ship (and vice versa) including comfort stop.