How long ago did you plant the Sweet Sunshine? If you wait a few weeks to plant something else that has about the same 77 DTM as Sweet Sunshine it shouldn't matter what variety because they won't be tasseling at the same time.

SH2 (supersweet) can be planted with any other SH2 variety. They may cross pollinate but it won't ruin the quality or taste. Sweet Sunshine is a yellow corn and if it got pollinated from a white SH2 variety you might get bi-colored ears but it will still taste fine and be tender. If it was cross pollinated by a SU (hybrid sweet) or SE ((Sugary enhanced) you probably won't care for the result,

Concur with Jack. I also had germination problems with Burpee seeds this year (English peas) must be a bad year for them.

I double seeded my Ambrosia that I bought in bulk locally. Treated seed and still had some skips and not too many spots where both seeds germinated.