Hello,
regarding the challenges to your friends shipping RIFs from abroad. I’ve played in Spain, Portugal and attended the Operation Rising Sun games in Croatia, and had no issue with the RIFs being in cases and checked in as hold luggage.
The key is communication, to check with the airline, and the host countries rules, and discuss it with them several weeks before you travel. I’ve had to print off an email or two from European countries with translations of what I’m travelling with, which does make it easier.
At the worst, most airlines will charge it as ‘Sporting Firearms’, which will cost the same as checking in a set of golf clubs.
I had one incident at Stanstead back in about 2010ish when the police just wanted to check them, but there was no problem.