Hi @JamesElliott,
Thank you for your posts and welcome back to our community forums. We're here to help.
If you're transferring a number from one network to another then the SIM card it's initially on will deactivate the moment that the port has been completed. You won't then be able to move another number onto that SIM card. You also wouldn't be able to do simultaneous ports, as these will happen on their own accord in the 24 hour period of the port date. I'd recommend doing them one by one to avoid potentially losing a number, but once a SIM card is deactivated you'll need to order a new one from that provider first to transfer onto.
I hope that helps, but if let us know if you need any further assistance or advice.
Thanks,