In this circumstance I would "downgrade" myself to the standard service. If I want to keep the group together, I'd go with what they are normally entitled to, i.e. ET, no fast track, no priority boarding. No skin off my nose to do so, and in fact I often don't even use the premium check-in anyway, depending on where in T5 I pop out.

I do no think the privileges were ever intended to be shared with a large group, and I also do not feel that I have any right to impose my >1 fellow travellers on others who are entitled to use the enhanced services. The mere act of a large group using the enhanced services will delay others who are entitled to use it in some ways or another, and that is not fair on them.

It is also potentially inconsiderate towards those in my group if I tried to lead them to priority lines etc and are refused and cause them embarrassment.