Wiring a sub-panel with an equal sized breaker on each end of the feed, which will trip first?
If you're anticipating overload, this is a sign you've underdesigned your electrical system

The fact you are anticipating breaker trips from overloads is a sign you are about to underprovision the circuit in question.  A better alternative would be to simply provision more power to the location; I would simply trench in a 2" PVC conduit, as that will let you run as much power as you'll ever need out to your tiny-house, anything from the RV-sized 30A@120V you're considering to a full 200A residential service, with a simple change of wire and breakers required if you want to upgrade later.  (Using direct buried cables means you have to dig up the cable in order to upgrade, and who wants to rent a trencher again six months down the road?)

Selectively Discoordinated Breakers (or, don't try to make any guarantees here, because you can't)

In most electrical distribution systems, there will be at least two breakers in series between the service point and any given outlet (light fixture, receptacle, etc).  This means that your situation isn't all that odd.  However, you cannot make any guarantees or predictions about which breaker will trip first here, as the properties of breakers connected in series are complex to predict.  Unpredictable dynamic arc impedances during the trip process, variations in magnetic trip coil and contact timing, and tolerances during thermal trip calibration all will cause variations in breaker trip timing.

This is undesirable in some situations, such as those involving emergency power systems or continuous industrial processes.  Hence, the major makers of commercial/industrial (i.e. molded case) circuit breakers publish tables that can be used by an engineer to select compatible sets of circuit breakers from the same model and series so that the furthest-downstream breaker trips first on a short circuit.  This process is called selective coordination.

However, it's considered impractical to selectively coordinate the loadcenter-type miniature circuit breakers used in residential and light commercial applications; their trip characteristics are not as well documented, and selective coordination requires significant engineering effort vs. the mere nuisance an upstream trip poses in a residential environment.  Compare this to the stakes of an inadvertent feeder trip in a hospital emergency room, where critical life-support equipment could be taken offline, or a continuous industrial process, which could cause a serious safety hazard due to a disorderly shutdown.

There is also the factor that selective coordination only works for short circuits; in fact, the upstream overcurrent protection device needs to be somewhere around twice as large, or larger, to have a hope for selective coordination to work at all.  Two equal-sized breakers simply cannot be coordinated on overloads due to the limitations of trip calibration.