There is no need to neuter two boars who live together, it won’t change their behaviour. All neutering does is stop pregnancies.
The benefit of doing it now is that they will undergo surgery while young so will be stronger for the anaesthetic but also that when the time comes that one passes, you will have the option to bond the piggy left alone with a sow immediately.
The cage extension means their cage is now 14 sq ft (if I’ve done the conversion properly!) which is a much better size for two boars. Ensure all the hideys have two exits, so they can’t get cornered by the other piggy. Ensure you respect their hierarchy by handling the dominant piggy first. I’ll add in some boar guides below
A Comprehensive Guide to Guinea Pig Boars
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
Neutered / De-sexed Boars And Neutering Operations: Myths, Facts and Post-op Care