Pull the key as usual, use different keyers and mix separate areas as necessay. The main problem solving is in the color adjustment. Despill/unspill/recolor the semitransparent areas so that they blend nicely with the background. There are a lot of methods for spill suppression and recoloring, the advanced keying breakdown series for Nuke is one of the best free sources, most techniques can be applied in Fusion the same way. Link to the first video in series: