I cannot even fathom a so-called enthusiast on this forum recommending to sell both for a damn minivan... Boggles the mind. I would never make that recommendation no matter what the circumstances are!
You only live once, if both are a burden financially sell the FJ. If you can easily afford both, and add to that consideration the a possible fuel price spike near 2008 levels in 2021, then keep both. The GX will take those miles in stride. Prompt regular maintenance would be a necessity @ 35k miles per year.