My two teenagers stopped bickering this summer. They play chess every night instead

Our son is 16 and our daughter is 15, and for the past two years their main shared activity has been arguing over the bathroom and the TV. In May, during a power cut, they found my old chess set. They have played most nights since, at the dining table, with a running score on a sheet stuck to the fridge. School starts again soon and both have heavy years ahead. I'm tempted to find them a club or a weekend tournament to keep it going. My partner thinks turning it into something organised would kill it. Is there a middle option, or should I leave them alone and buy a second board?