[@robin-w Moderator 4 years, 11 months ago]

you can make a topic ‘super sticky’ which will make it appear at the top of all forums.

I know of nothing that will do a couple of forums, and indeed the code to do so would need to catch lots of areas, such as subscriptions, freshness etc. which at the moment rely on the ‘post parent’ table element of WordPress, so lots of code might be needed to get it to work.