Studying gamma-ray emission by Galactic objects is key to understanding the origins and acceleration mechanisms of Galactic cosmic ray electrons and hadrons. The HAWC observatory provides an unprecedented view of the gamma-ray sky at TeV energies and is particularly suited for the study of Galactic objects. However, the interpretation of the measured data poses several challenges. The high density of sources and source candidates can cause source confusion and make it harder to disentangle the origin of the emission. The relatively low angular resolution of HAWC, compared to instruments in optical or radio wavelengths, can further cause the emission of neighboring sources to bleed into each other or even make them look like one extended source. On the other hand, with its wide field of view, HAWC is uniquely suited for the study of extended sources. However, this requires the simultaneous modeling of both their morphology and emission spectrum. Joint likelihood fits to data taken over a larger range of energies can help overcome these challenges and achieve the full potential of the HAWC detector. In this presentation, we will discuss how systematic uncertainties related to joint likelihood fits can affect the measurements.