Visit to Nezu Shrine and Kameido Shrine

We are interested in seeing the azalea festival at Nezu Shrine and the wisteria at Kameido Shrine on April 15 when we are joined by a friend who is arriving at Haneda airport at 12 noon. After visiting Kameido we like to stop by Kinshicho to shop at Daiso.

1. From Haneda airport, what is the best transportation route to Nezu. We prefer not walking great distance. There will be four of us so we could consider taxi rides if it is faster and more convenient. Do we have to be concerned about heavy car traffic that would make it easier to travel by subway/trains.

2. Would it work out better to visit Kameido first and then Nezu (although Nezu Shrine closes at 5:30 pm).

Thank you for your assistance.

For going to Nezu Shrine, you could get off at either Nezu Stn, Todaimai, or Sendagi - either of them is about a 5-minute walk to the shrine. For understanding how to get there, fares, transfers, etc, look at Hyperdia.
http://www.hyperdia.com
If you arrive at 12 noon, it will take you at least an hour to deplane, get your bags, and go through Customs & Immigration. If time is a concern then go to Nezu Shrine first.
As for Kameido, you might be too early for the wisteria. Normally it starts towards the end of April and Golden Week (the first week of May). With the weather these last two years, you could get lucky, but no promises.
If you want to see some beautiful flowers, you should also consider going to the Hitachi Seaside Park and the Showa Kinen Park.
https://en.hitachikaihin.jp/
https://www.japan-guide.com/e/e3034_showa.html
Your timing should be very good.
Also, Tokyo has a number of beautiful traditional gardens worth seeing. Some have a history going back centuries.
https://goo.gl/tAECfM
You'd also be in time to see the "secret" garden at Sensoji, Denboin, only open a few months a year.
https://goo.gl/q5nDom

Thank you Ken, for your wonderful suggestions and advice. We will definitely visit Denboin Gardens and the Showa Memorial Park.