These work really well in tight spaces. The pipe gets clamped in the tool so won’t move.
AB Tools Brake Pipe Flaring Tool Professional In-situ 3/16" SAE Hand Held FL29 https://www.amazon.co.uk/dp/B01M4RC2YW/ref=cm_sw_r_cp_tau_Zi32EbWW39JCB
I used the exact same flaring tool on an Almera Steel pipe , so it's definatly doable maybe use a little wet and dry between tool and pipe to stop it slipping ??