Sweetcorn

You can grow two if they're the same type. Discovering the types of each seed can be problematic, the seed merchants don't always specify.
I'd go with Earlibird for the big one. I've never bothered with a small one, too much faff for not a lot of return. By all means sow early if you think you can get away without frosting. I sow early May, you may get away with late April. Plant in blocks rather than rows (as if!) so they pollinate each other.
Have a look here https://gardenfocused.co.uk/vegetable/sw...ieties.php for some basic info. It looks like Earlibird and Goldcrest are the same type so might not need isolating from each other. I'd grow in blocks of 3x3 or 4x4 depending on how many you're planning to grow. I usually try to do 2 blocks of 5x5 or 6x6 staggering the sow dates but have found thy catch up with each other.

I sow in root trainers to allow long root growth like you would sweet peas. Hen they can be transplanted with minimal root disturbance. I'm told sweetcorn don't like root disturbance but once when someone gave me a pot crammed with 8" tall sweetcorn plants, I separated them and they grew on ok.