If I enroll for self plus one, may I decide which TEI family member to cover?

Generally, yes, as specified in § 894.202. However, if you are an enrollee and you do not elect a type of enrollment that covers a TEI family member, that TEI family member will not have FEDVIP coverage or benefits. A TEI family member who is not a TEI certifying family member may not self-certify and enroll himself or herself as a TEI family member in a FEDVIP plan. Note however, that a TEI family member may seek reconsideration of an erroneous enrollment under § 894.104, and the Administrator and OPM retain authority to correct enrollments under § 894.105.