You can use an invocation of God’s blessing if you are not ordained (meaning: you do not bless, but ask God to bless, and you do not trace the Sign of the Cross, but you sign yourself).
Sprinkling of Holy Water is a different story. Holy Water is a sacramental, already blessed. One can use it anywhere, unless there’s a legal reason against it. There may be some legal prohibition against spraying liquids on people.
[Also people that are not part of the group, like the “patients”, may find it rude ]