I have some of these roughed out as I'm not sure how many days we would need in these areas

Day 1 ~ Arrival day in Auckland, then fly to Blenheim. Pick up rental car and stay Blenheim for 1 night so we can crash without driving far

Day 2 ~ sleep late, vist a winery or two (or three) then drive to Picton, stay 1 night

"so we can crash without driving far", lol.

Blenheim and Picton are only about 25 minutes apart, but if it were me, I'd allow two nights minimum in Blenheim. This will give you a full day to explore and visit wineries (or take a winery tour) and not have to worry about driving to Picton impaired.

I find it takes awhile to get my bearings in a new area and a lot of time can be wasted finding one's way around, etc, especially having just arrived and still getting used to left side driving, etc.

Picton has a lot on offer despite it's tiny size - taking the mail boat into the sounds, or taking a water taxi and walking a section of Queen Charlotte Track are popular options. Do you have plans for Picton?