You are taking the fun out of gardening...lol You are definitely over thinking this. Tomatoes are weed plants, they will find a way to grow....anywhere! If your seedlings are getting real leaves, the seeds are not the problem. Plants only need three things to grow; sunlight, water, and nutrients. The fresh soil provides the nutrients, the grower (you) provides the water. What is the last thing missing???? Sunlight! They can't stay indoors without full sun, that's 8 hrs of full sun at least and more is better. That is all they need to grow and propagate fruit. As you have stated above, they die off after they get their true leaves.... they are telling you, They need something; sunlight!Red Spider Mite. Have looked over 3 plants very carefully and do not see any bugs. For the red spider mite, apparrently holding white paper beneath a leaf, gently shaking, then use a ______glass for a close up look. RX is soapy water.
All the pics showed well established plants. Often healthy ones side by side with a pale green plant.
On my plants, die off starts after true leaves have appreared; Seems to happen to all the plants at once; then tips of true leaves start to wilt.This is about 60 plants!
If these all die off, I can still try a couple other options.
New pots, perhaps shorter, squatter type.
Microwave or oven treat potting soil.
Set up in new area.