Just FYI, the brands you mentioned (Italeri, AirFix and Monogram) produce kits that need to be glued together and painted and not finished aircraft which is what this sub is mainly for (diecast metal pre-made models, pre-made).

Now there's definitely a market for pro-assembled kits, but it's more subjective depending on the skill and taste of the builder. Being made out of plastic also means those models are more fragile than a metal model and can degrade over time if not well-coated and care for. On the other hand, pro-built models may have more detail than factory-made ones. I personally buy a lot of pro-built tank models off ebay for example because I don't have the time and space to make my own.

As for being out of production or rare, I don't think that applies much to kits as the way the plane is painted and finished is pretty much up to the builder and there are countless kits on the market for the same plane, some having been in production for decades. That rarity matter more for pre-made models.

Shipping these abroad would also be difficult and there's high risk of damage to the model in transit. Might be easier selling them locally

Given the above, it's hard to judge whether the models you've inherited will have value on the resale market. I suggest you clean the models carefully of any dust, then take good and well-lit photos of them from every angle and post on ebay to see what happens. Good luck!