Ok, first off it's very unlikely there are issues with each individual lock actuator in my opinion. Just seems very unlikely to me.
As for the sending unit/fuel issue. This is worth your money to have them investigate. You can likely change either of the problems they are suggesting and of course, an independent shop could also do the work to say you some money. If it's the gauge, it's that expensive because it's the whole instrument cluster. The sending units, one is just a sending unit, the other is the fuel pump module and sending unit. Before you sink any money you want a proper diagnosis. That would be worth the money.
The rear hatch, if you can open it, it's not a huge job. You do have to remove the interior trim, then in all honestly its only a few bolts holding it in place and it is as simple as un bolting, disconnecting a couple cables and electrical connections and just reversing the procedure when you put it back together.
Usually it's about an hour to do that one.
Their labor charges seem a bit high but not HUGE, mostly parts are the cost. You could use an independent shop and aftermarket fuel pump and sending unit to save some money there.