We present new and archival ALMA observations of two strongly lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope Survey, SPT0418-47 (z = 4.225) and SPT2147-50 (z = 3.760). We study the [CII], CO(7-6), [CI](2-1), and, in SPT0418-47, p-H2O emission, which along with the underlying dust continuum are routinely used as tracers of gas mass and/or star-formation rate (SFR). We perform a pixel-by-pixel analysis of both sources in the image plane to study the resolved Kennicutt-Schmidt relation, finding generally good agreement between the slopes of the SFR vs. gas mass surface densities using the different tracers. Using lens modeling methods, we find the the dust emission is more compact than the line emission in both sources, with CO(7-6) and [CI](2-1) similar in extent and [CII] the most extended, reminiscent of recent findings of extended [CII] spatial distributions in galaxies at similar cosmic epochs. We develop the [CI](2-1)/CO(7-6) flux density ratio as an observable proxy for the gas depletion timescale, which can be applied to large samples of DSFGs, in lieu of more detailed inferences of the this timescale which require multi-wavelength observations. Furthermore, the extended [CII] emission in both sources, compared to the total continuum and line emission, suggests that [CII], used in recent years as a molecular gas mass and SFR tracer in high-redshift galaxies, may not always be a suitable tracer of these physical quantities.