If I heard them correctly they said that in the show they have to climb all over the barricade during the battle scene and then sing 'The People's Song'.
No they don't!
'The People's Song' is in Act 1 (with a reprise right at the end of Act 2, WAY after the barricade stuff is over) and the barricade is in Act 2!
Yes Enjolras has to wave the flag whilst at the top of the barricade, but he doesn't sing that. All he sings is "Let others rise to take our place, Until the earth is free!", then the finale battle starts, at the end of which Enjolras grabs the flag and waves it before being shot. It's gruelling, but you certainly don't have to sing a full song which is what they implied.
I've no experience of the barricade myself, but I will tell you that that bloody revolve is a nightmare to work on!