add 2 extra radiators to 8mm flow and return?

yes you can but 8mm aint big enough you will have to increase to 15mm then run to the room you want it in .first you need to drain the boiler.then run your pipe i use compression fittings myself ,once you fitted rad to wall run pipes to meet it then fill boiler and dont forget to bleed every rad in the house

chris
January 2009