Skinning and animating characters

We are a company that does Flight Simulation products and are looking to add passengers/pilots to our aircraft. To that end, we have around 20 characters that need proper skinning (base skinning is done on some but the envelopes need tuning; Others need the full treatment). Some of the models do not have heads. Heads from the other models should be chopped off and placed accordingly. Some of them will need animation walking up a defined set of stairs and climbing into cockpits. Some of them will need to be placed into seats, waving, pointing, shifting around, and minor head/arm/hand/body movements. Some will be required to move hands/arms/head in conjunction with aircraft movement. We will supply the stairs and the seats. All animations must be split up in the timeline. Eg: head turns left/right 0-100, head goes up and down 101-200, left arm goes up/down 201-300 etc We are looking for someone who has experience. 3DS Max 2018-2020 is a requisite as Biped is a must.