Pretty sure that without hacking XP it only supports a single inbound RDP session, so even if your application was multi-user friendly your OS isn’t.
For 10 users you’ll need 10 separate XP VMs each with your application software, unless you find some other method.
This isn’t really a question for a VMware user forum though, the fact you’re running XP in a VM doesn’t sound relevant to the issues.
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