I think your receiver code still suffers from the same problem. If the correct serial data is received, you will set Spark and Solenoid LOW. Next you check the button which is not pressed and you set both HIGH again.
@Dansky
You need to add some information. If your Spark and Solenoid are activated (either remotely or via the button), how do you switch them off again. Based on your code, they are activated as long as the button or the remote button are pressed; when you release them, they are deactivated. Is that how you want it to work?