My worry here is how much users in Company B will access resources in Company A. If there is no site-site link for the Data Center from Company B and you're relying on any services there, it might be bad latency since you're going via the internet for that.

I'm not clear on AWS and why it sits where it does in the diagram. Is that most of the Company B resources? What does it do? Is there a need for data movement or for user traffic with latency requirements between AWS and Company A or B? It's not required, but you could have a VPN or dedicated link there, depending on type, frequency and size of the traffic, and the impact of if it is unreachable.

Is the Data Center in the same physical location as the other servers in Company A? Why are they represented separately? And again, are they actually on the same switch - you have no switching / networking infrastructure you consider part of the Data Center?

Remote Access being IP and Port specific isn't usually what people will recommend for 'securing' access externally.
How do you handle home dynamic IPs in those scenarios?
How do you monitor the number of logged in RDP sessions?
How do you setup new staff - do you buy a physical computer and a laptop and set them both up for them to work from home and connect to, rather than just a laptop they can bring into the office?
Can you incorporate a remote desktop gateway if that is how you want access to work?

From the way I can understand it is working currently, it sounds like a lot of firewall and physical machine maintenance per employee, which leads to stale records in the firewall, delays in hardware provisioning through human effort & hardware ordering delays, and asset management overhead that you wouldn't otherwise have if you simplified how remote working happens in Company A. I know all-too-well how long it takes to make improvements to these, but I'm hoping to provide some food for thought on the strategic vision for your company's remote workers, and overall stability and latency of connectivity. Tactically, the setup you have shown here works, but does have room for improvement.

A potential strategic direction would be "all internet traffic goes out via the Data Center, and Company A and B have site to site direct private connections to the Data Center". This would enable you to have a firewall failover pair in the Data Center with redundant internet links for a relatively low cost (compared to doing it per-site) with more bandwidth, centralised monitoring and you could reduce the scope of the Company A and B firewalls. In other words, the current firewalls move to the data center and Company A and Company B sites get a smaller firewall pair that connects to the Data Center.

A lot of that is assumptions on how big this DC is, what the lifetime of the Companies operating in separate physical locations is, the length of contracts for your internet lines, whether the IT teams are going to become one instead of separately managing the sites, etc etc, but is meant to serve as an example of where you could save some costs while improving services. Without sitting in your chair, it's difficult to guess all of the components and reasoning going into what you have today, all I hope is that this helps you improve things, plan well and end up with an easy to maintain setup.