How do airlines handle their non-standard passengers for the load control process?
Airlines are responsible for weight and balance control programs. In the US, FAA AC120-27 describes how these work, and it specifically describes the treatment of special passenger groups like sports teams:


What are the standard average weights for special passenger groups that do not fit an operator's standard average weight profile?

a. Sports Teams.
(1) Actual passenger weights should be used for nonstandard weight groups (sports teams, etc.) unless average weights have been established for such groups by conducting a survey in accordance with the procedures established in Section 3 of this chapter. When such groups form only a part of the total passenger load, actual weights, or established average weights for the nonstandard group, may be used for such exception groups and average weights used for the balance of the passenger load. In such instances, a notation should be made in the load manifest indicating the number of persons in the special group and identifying the group; e.g., football squad, etc.
(2) Roster weights may be used for determining the actual passenger weight.
(3) A standard allowance of 16 pounds per person may be used to account for carry-on and personal items as provided in the operator's approved carry-on bag program.
(4) If the carry-on bags are representative of the operator's profile but do not meet the number of bags authorized per person, the operator may count bags and use a 16 pounds per bag allocation.
(5) Actual weights must be used in cases where the carry-on bags are not representative of the operator's profile.
b. Groups that are predominantly male or female should use the standard average weights for males or females provided in Table 3-1.
c. Military Groups. The Department of Defense (DOD) requires actual passenger and cargo weights be used in computing the aircraft weight and balance for all DOD charter missions. This requirement is specified in DOD Commercial Air Carrier Quality and Safety requirements (reference 32 CFR part 861, section 861.4(e)(3)(ix), as revised). FAA-approved air carrier weight and balance control programs may be used to account for carry-on/personal items for mixed loads of military and their dependents (such as channel missions). For combat-equipped troop charters, the Air Mobility Command (AMC) will provide guidance to account for the additional weight. If aircraft operators perceive that the weights provided are understated, they should seek confirmation of the actual weights and should make reasonable upward estimations and adjustments to those passenger and/or bag weights.

In other words, use actual weights or come up with an appropriate method to determine appropriate average weights for special groups.