I'm assuming this is relating to blaze spawners found in prison. They can only die "autonomously" to drowning in this server. To kill them, I would suggest making them falling into a 2+ block deep hole filled with water, to which they will sink and eventually drown. If you want me to show a visual demonstration, just dm me @Kan#6969 .
As above. Blaze don't take contact damage from water, however, they do suffocate after their first tick of drowning damage, so you can either drown them in a 2 deep pool of water, or you could crush them with Redstone.