MAT01 Matched NPN Transistors - Substrate bias voltage
The substrate will be a fine node to inject noise / trash / VDDspikes into your circuit.

Model this IC, for this purpose, as 100 pF capacitors from substrate node to each collector node. The collectors are in a "tub" or a well, surrounding the base region which surrounds the emitter region. The collectors are easily 20X by 20X larger (400X the area) of the emitter.

I suggest you use an RC lowpass filter to bias the substrate node to the most negative. Use 1Kohm and 1nanoFarad, if your noise injection modeling (using the 100 pF I suggested) shows the noise currents (from VDD spikes of a switching_regulator) will upset your signal chain.

The datasheet may show collector_to_substrate values greatly different from the 100pF value I suggested. Notice the datasheet value is at a HIGH voltage, such as 20 volts. Thus 100pF is more conservative. 

Use the RC lowpass only if you need to. First task is to prepare an error budget, with awareness of your signal bandwidth and of the risetime of spikes on your VDD.

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Examining the MAT01 datasheet, there is no data given on C_substrate_collector, though the case is tied to the substrate. I'd assume 100pF in any simulation.
The datasheet shows 8pF collector-to-collector, thus the substrate_collector is at least double that, or 16pF.

The collectors are tied to the case, which is 9 mm across.

Thus the case is a fine metal object to gather electric field flux, and inject those displacement currents into your circuit.

The case is approximately a square centimeter of area.
Assume a switching power supply 1cm away, with 10 volts in 10nanoseconds slewrate. What is the current injected into the case/substrate/collectors?

Using parallel_plate model (and ignoring fringing), the capacitance thru the air is

C = 9pF/meter * area/distance = 9pF * 0.01 = 0.09pF

The injected current is (using Q = C*V, differentiated to be I = C * dV/dT with constant C)

I = 0.09pF * 10 volts/10nanoseconds

I = (0.09 * 0.001 * 1nF) * 1v/1nS

and cancelling the 1nF by the 1nS

I = 0.09 * 0.001 = 90 microAmps of spikes / trash / noise injected into your collectors.

Does your error budget allow that?