I'm in a middle of designing an application to be used by two parties in such a way the involvement of the second party is more of a guide to the first party e.g. children & the parents, addicts & their sponsors, etc. It is entirely possible for one second party to be a 'guide' to more than on first party.

My question is on the whole username/password pair design. The status-quo is each having own username/password pair and the second party once logged in, gets a list of first parties he/she is a 'guide' to, etc. While this works, I believe sharing a username (obviously keeping passwords separately), could improve the UX of the app: i) In real life, this is how we share bonds: Family (Shared last name, different first names), Sports teams (One team name, each team member usually gets a nick name), etc. So you could think of the shared username as family/team name and the password as first name/nickname. ii) By sharing username, the second party only has to login using the username he/she is sharing with the first party and does not have to go through the process of first login him/herself and then selecting the first party.

Anyways, is this a good UX design or I've just had too much coffee?