Multiplex two I2C ICs into four 7 Segment displays
Yes, there is a way to control four 7-segment displays with two PCF8574AN chips.

Nearly all multi-digit 7-segment displays use some kind of multiplexed display.
If you have common anode 7-segment displays,
you could use something similar to the circuit in Figure 2 of Atmel appnote AVR242:

One PCF8574AN drives the particular segments to light up.
perhaps P0 through a resistor to segment a, P1 through a resistor to segment b, ... P6 through a resistor to segment g, and P7 connected through a resistor to the decimal point.
(Every "segment a" pin of every 7-segment modules would be connected together, etc).
It appears that the PCF8574AN can sink IOL = 10 mA per output pin, so it can directly pull down the low side of those LEDs.

Another PCF8574AN selects the current digit to light up by turning on a transistor connected to the common anode of the selected digit, and turning off all the other digits.
It appears that the PCF8574AN cannot source much current IOH, so it needs a transistor to pull up the high side of those LEDs.
It looks like almost any logic-level pFET such as VP2106N3-G, a ZVP3306A, TP0610, or BS250P or almost any PNP transistor would work.
If for some reason you only had nFETs or you only had NPNs, you could probably figure out how to get that to work.

Those 2 chips could control up to 8 digits.
The tricky bit is scanning through the digits rapidly enough to maintain the illusion that all the digits are glowing "at the same time", while also taking care of whatever else your project needs to do.