Unless otherwise indicated, whenever notice is required under this Chapter, it shall be given pursuant to this Section. If a client is under 18 years of age, notice shall be given to his parent, guardian or person in loco parentis. If the client is 18 years of age or older, notice shall be given to the client, his guardian, if any, and any 2 other persons whom the client may designate. If the client is 18 or older but lacks sufficient capacity to understand and consent to the designation of persons to receive notice, notice shall also be sent to his nearest adult relative.