Let your still green sweet pea seeds ripen before using.
To improve germination of sweet pea seeds, soak for 24 hours in water, transfer seed to a container lined with kitchen roll and cover with another piece of kitchen roll, keep moist and wait 5-7 days for seed to start germinating, then sow in pots.
I lost all my own saved sweet pea seeds to squirrels this year - I had wondered what was taking them and a couple of days ago saw a squirrel in my greenhouse eating them, I also lost all my 'corn cockle' seeds and suspect squirrels are the culprits!