You can use the same account on different Switches, but you can only play on one at the same time with this account. You can always play on your main Switch, but other Switches that use the same account must at least every 3 hours connect to the internet to check if the main account is used, if so games of this account on the other Switch(es) Go to pause.
Its the most consumer friendly family sharing of the current consoles (Switch, PS4, XOne), but it has obviously disadvantages for the secondary accounts.