[Warning: this post is mostly wonky referee talk]
In my personal opinion, I like allowing waiting team members to hold attachments.
Nevertheless, when using GP2, it is important to review all details.
R12 Storage very clearly says "must stay in view of the Ref," which might or might not be true for non-Technicians holding Equipment.
We advocates of allowing team members to hold Equipment also look at the words "on a stand" to see if that can be interpreted as being an example rather than a requirement.
So the bottom line is that your team can practice with having non-Technicians holding Equipment, but you should be prepared to use everything off a stand, if required.
For what it's worth, if your team is at one of my tournaments, I will be lenient on teams holding their own Equipment, but I will require all Mission Models to stay near the table and Technicians. If people take issue with that distinction, then I'll require everything in Storage to be under the control of the Technicians.
[I've talked about this at even more length in discussions with other Referees, which shows that it's a tricky interpretation.]
One important takeaway from this for your team, is that your team needs to read and understand the Rules, Missions, and other documents. If you cannot point to words on the page to support a request, then you usually won't get what you are asking for.
Virginia-DC FLL Referee Advisor