I would not plant two seeds in one pot unless you plan on leaving them alone, or killing one without digging it up. Why not put individual seeds in some small container like a yogurt container or something?

If you have different height plants under one light, you need to have stands or some way of changing elevation on individual plants so that you can keep the canopy uniformly as close to the light as possible. If one is and one isn't, the latter will either look like it's hibernating or stretching like a lanky string bean giant. Otherwise you can keep topping the tall one, but you'll end up with one stringy plant and one bushy one.

What kind of 100W light? For 2 plants that might just barely be enough if you are talking about true fluorescent watts and not incandescent equivalent or HID. Don't for get the correct color lights for veg and bud. This is more important than most people realize IMO, especially those new at this.

Got pictures?