I mean I guess it depends on what you define as transitioning smoothly ... as in graphics? Overall presentation? Mechanics? Innovation? Sales? Reception? If we are to consider Let's Go a smooth transition, then yes, all these developers should be fine. Though Intelligent Systems is hopefully making Fire Emblem Three Houses look a little cleaner by now.
My predictions in terms of sales.
Fire Emblem: 5-6M
Animal Crossing: 20-22M
Luigi's Mansion: 7M
What makes you think AC will sell that much? I can see it getting close but 20M?