I think it would be better for you to setup Direct Routing for these users instead of splitting users into two different tenants. With different tenants users will be treated as two different organisations and not as the same.
You’ll want to keep the users in a single tenant to take advantage of the collaboration apps like Teams and SharePoint as well as unified GAL, reporting and analytics. A single tenant will also have a much lower Total Cost of Ownership (TCO) as it would be easier to Manage and support.
Direct routing is certainly the best option in this scenario.
We are an independent provider offering direct routing for MS Teams. You can connect our SIP trunks to Microsoft Teams via a virtual Ribbon Session Border Controller (SBC), enabling your employees to make and receive external calls without requiring Microsoft Calling Plan licenses or on-premise equipment. We are fully skilled in this type of deployment, and we have rolled out a number of systems already for small and large organisations.
We host the SBC in Azure – this then routes to your 365/Teams account and DID numbers will be allocated using PowerShell. Our SIP trunks are delivered directly from our own network. Because we peer directly with Azure, where we host the MS Teams certified virtual SBC; this brings Infinitel on-net with Microsoft. The trunks we provision from Azure are all Infinitel owned.
We take care of all number porting and provisioning requirements. (We can provide DID numbers, local dial-in presence, and management of call routing to emergency services in hundreds of international destinations)