Subordinate makes more than me, fewer responsibilities and I am in another country. What to do?

Reserving some details to avoid giving identifiable information:

I am outside the USA, the company I work for hired me a while ago to replace someone from there, let's call them Sam.

My role was to replace Sam and eventually do the same tasks for Europe and eventually Asia. Sam did not do the tasks alone, he had some people under him to distribute the load and coverage (otherwise he wont be able to sleep).

Sam has been moved to a new job with fewer responsibilities (before in charge of all Americas, now only a single subsidiary). I am happy for him since he has kept his same salary.

Sam is a great guy, he understood that I am not his enemy that this was due to the company management, he has trained me well, he has made himself available to be consulted on stuff that happened in the past, or ongoing stuff.

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But here is were things become awkward, starting next month, Sam's new role will be subordinated to mine:

1. Due to the company bureaucratic configuration, I only have a single person from the Americas area to cover Sam when he takes vacation time, sick leaves, PTO, etc… But I can not order Sam to cover or aid us in the general Americas tasks (he knows what to do,, he is willing to help, he is not allowed by higher ops).
2. I will have more tasks to supervise and execute day to day, and I will have to overload myself and/or the other authorized person when Sam is not available.
3. Given that I am in another country my salary has always being lower than his but I will be in a position that an underling has fewer responsibilities than me with a vastly higher salary.

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What to do?

First and most important, I need to be able to move Sam and the other person around, otherwise the load is uneven and we will fail at some point. I have spoken to my boss about this, but no resolution yet.

Second, Sam is a pro, but I need to know how to handle that he basically trained his boss. He is laid back so I don't expect any personal issues but I need guidance on this.

Third, I need to see how I fix the monetary compensation part for me, I can not expect to get Sam's salary converted to my currency but I will be having more responsibilities and the salary disparity is grating (converted to my currency, Sam makes between 3 and 4 times my salary, the variability is due to exchange rates and other benefits).

Any advice?