Looking for some paint-able models of trains

I have 2 nephews who are polar opposites;

The first is very into painting Warhammer. We have managed to form a nice little bond over it and i love spending afternoons with him building and painting his models (8y/o) while he chews my ear off about things that he has learned about it.

However, his brother (10y/o) is really interested in trains (autistic special interest.) He doesn’t have space for a train set and he already has most of the paraphernalia but i would like to get something so that i can spend time with him as well, or better both of them at the same time.

I was wondering if there are Airfix model kits or something similar (brand doesn't matter, Airfix is just what comes to mind,) that i could buy for him to spend some time with him AND his brother so he could be building and painting a train while his brother was painting Warhammer.

Web searching has failed me and doesn't seem to have any ideas for me so i thought i would come here and ask the experts. He isn't into any specific trains though he spends most of his time playing train simulator with 'modern' trains.

Thank you in advance. I really appreciate any help, just trying to be the best uncle i can be. :)