My friend want to run 2 knight

Me and my friend is running a 2000 point tau vs salamander but he want to bring 2 knights Knight Castellan and Knight Paladin he recently just got those knight and I understand he wanna play both of them but storm surge seems pretty weak against those 2 and I only have one hammerhead and a sky ray gunship should I allow him to do it? If yes, should I add more hammerhead