As they sit, probably each kart ~ 1,000-1100 at best.
You’re about right. A used Kt100 that isn’t ‘fresh from a builder’ is worth ~350-400 at most.
If you separate the engines, you likely will be able to sell them for that price after continually renewing the listing on Ebay, Ekartingnews, here, etc.
However, if you do that, it will be almost impossible to sell the karts. So, for that reason, you may want to consider not separating.
That said, both chassis are pretty dated, so finding a buyer can be tricky.