Please consider what the weather is like in February in northern Europe. It will be cold, gray, dark and probably drizzly in places like Amsterdam, London, perhaps even Paris. Also, daylight hours are still relatively short. For instance, in Amsterdam on February 15, 2022, sunrise is not until 7:57 am and sunset is still before 6pm.
Also consider COVID. Europe is suffering a big increase in cases now; there's no telling what the situation will be like in February, so planning is difficult. But for sure, you both will need to be fully vaccinated and be able to show proof of vaccination for entry to museums, restaurants, bars and other attractions.
And I would most certainly agree that 9 days is only enough time to see a little of 2 or 3 neighboring countries, not go flying all around which would require you to spend far too much time in airports and not enough time seeing anything. For better weather and more sunlight, try Spain and Portugal. Or just Italy.