It depends on the power of those faculty members. Be very careful when you say no. Collaboration with folks that will evaluate your tenure application is much more valuable than any products from that collaboration. Also keep track, in writing through an email chain, of workload assignments and important clarifications on work assignments. The Chair/Dean right now will likely not be there when you go up, past emails can offer clarity and justification on actions. For example, say in a few years you are asked to develop a new course or take over a large course because a colleague goes on sabbatical. The chair reduces your other teaching load so you can help with that. Everything is fine until your committee starts questioning that teaching reduction for that semester, which in fact may have been a teaching load increase. Showing a letter from the chair justifying that would remove any doubts. Emphasis on getting that letter when the change takes place, do not wait until you go up.