I don't currently offer a library for animation retargeting. Thank you for that idea.
Before I charge ahead, I want to understand your use case a bit better. The big question in my mind is how similar those humanoid figures are, in particular how similar their armatures/skeletons are.
The 1st step in retargeting animations is simply converting the bone names/indices in the source skeleton to those of the target skeleton. For instance, bone #60 ("Calf.L") in the Sinbad model corresponds to bone #97 ("shin.L") in the Jaime model. With a little care in creating your models, you could avoid such issues, I suspect.
The 2nd step is re-orienting the bone rotations from one context to another. For instance, the local +Z axis of Sinbad's Calf.L points forward, but in Jaime it's the local +X axis of shin.L that points forward. Again, I suspect you could easily avoid such troublesome differences between your models.
Maud performs steps (1) and (2) using a "skeleton map". In general, the map must be created manually for each pair of skeletons you plan to use for retargeting. Maud makes it relatively easy to create maps, but it's not automatic except in the trivial case of equivalent skeletons.
The 3rd step is creating animation(s) in your target model and adding the retargeted bone tracks to those animations. If the source model and target model have equivalent skeletons, this becomes a simple cloning operation. You probably don't need a library for that! If the skeletons aren't equivalent, you'll need skeleton maps, but once you have them, the creating and retargeting can be automated.
The final step is fixing up the retargeted animation(s) to address issues like feet sliding or not touching the ground, limbs poking into the torso, and so on. Maud includes tools for doing this fixup manually, and I'll be writing more over the next few weeks. But maybe with a little care you can avoid such issues, too. Perhaps some experimentation is in order.