is there a direct train route or would we have to go through Paris to reach giverny by rail? Other options from Paris to Giverny without a car?
There is no rail service to Giverny. The nearest railway station is Vernon, from where there is a bus service. Trains to Vernon leave from St Lazare railway station in central Paris - from Rennes you arrive in Paris at Montparnasse, from where you can get Metro line 13 direct to St Lazare.
Rennes is on the line to Paris Gare de Montparnasse.
Giverny is served by Vernon, on the line from Paris Gare St Lazare.
It is over 4 hours, into Montparnasse, cross Paris to St Lazare and back out.
When you look up train schedules online from Rennes to Vernon, they will show the connection points, including transfer within Paris by taxi or metro. How to Look Up Train Schedules and Routes Online gives you the DB train schedule link and tips for using it.
pariscityvision.com and grayline.com both offer tours to Giverny.
I took a minibus tour there in 2011 and there were only three of us
on the tour (always a small group because of the size of the bus.
The van driver gave us quite the history lesson on the
way out there. When we arrived, he set us free to do the home and
gardens at our leisure and told us to return to the parking lot in 2 1/2 hours.
I really liked this trip -- choosing myself where to focus my attention.
No need to take a train and then catch a bus when they take you right to the door.
The minibus trip to Versailles is also very good.