add on sensors

It makes no real difference except I would join them together with diodes on the blues AND greens (bands towards the sensors) and plug them into the alarm's sensor socket,  then it's using the correct GWA from the socket.

True, it makes no real difference, but all the addons would be on constantly and triggering as well, except if the alarm isn't armed he won't know, they'll be on even whilst driving,

The tilt sensor calibrates the angle of the vehicle when you arm the alarm and it receives ground on the ground when armed input. If it is wired straight to ground, it is not working at all. It would also help if you listed the model of the tilt sensor. I know DEI has made a couple similar models over the years.

the tilt sensor is a 507M, the audio sensor is 506t and the prox os 508DKease

From the install manual for the 507m: IMPORTANT   In order for the 507M to learn the inclination angle each time the vehicle is parked, the ORANGE wire must be connected to a security system ground-when-armed output or to an acceptable switched ignition ground reference wire. Its not really important what the "ground" wires go to on the 508d or 506t. Connecting all 3 to the same GWA circuit would probably be more current than it is designed to handle. Boosting the output with a relay would not work either, because you would kill the vehicle's battery. Don't worry if these were wired directly to ground.

Just to make another point, you've too many sensors, they will interfere with each other unless diligently set up, all you really need is a prox sensor, the 507m is more reliable than the older 507t but make sure it's mounted on a solid surface.  Usually unless the 506t is turned down so much that it's unusable, the outer zone of the 508d can trigger it.