Venice Airport to Dorsoduro area of Venice

It depends on the size of "my family". When you figure that 14 EUR per person for the cheapest way to go (No 5 bus plus vaporetto), if your family is big enough, a water taxi could be a deal. Ca' Rezzonico can't be a bus station, but it is a vaporetto (aka water bus) stop. The Alilaguna is 15 EUR per person, and maybe the least scenic way to arrive. Part of the charm of Venice, city buses are actually boats.

You have several choices.
Water taxi, at about 110 euro for the group, maybe 120 euro.
Shared water taxi at 25 euro per person.
Alilaguna ferry at about 16 euro per person.
Land bus to Piazle Roma (8 euro) plus a water bus (vaporetto, 7.50 euro) down the Grand Canal to Ca’ Rezzonico.

We have used the shared taxi, the Alilaguna and the bus plus vaporetto. We have never explored our inner James Bond and taken a private taxi.

For me, it would be the land bus plus No 1 vaporetto. It gives you a ride down the Grand Canal. The Alilaguna ferry is a bit ordinary, low in the water, windows caked with salt. If you were a party of four of five, the water taxi would be a good choice.

A couple of things to note.
The Alilaguna is not a water taxi.
There are two fleets of boats, the Alilaguna and the ACTV water buses, the vaporettos. They are two completely different organisations. The Alilaguna is about servicing Marco Polo, the ACTV vap service is about commuting around Venice and the lagoon.

Confusing at first, but you will soon get a handle on it.

Katia knows more about Venice than your average tourist.
Thins is all about transport around Venice.

https://www.theveniceinsider.com/how-to-guide-transportation-venice/

Can you return the car to Piazzelle Roma area in Venice- then take vaporetto to your hotel?