Coolant leak. New water pump. Temp gauge going crazy

I just recently got this car from my mom. My bfs friend was supposed to look into it first it was head gasket then water pump. The water pump just got put in last night, but the coolant is still draining into somewhere and now the temp gauge is going from the red to below 100. I know I need a new thermostat for the temp gauge. Also when I turn the wheel too much to one side the car stalls out. Now it is whenever I turn to the right. Much needed help please and thank you!