I don't have any experience of this situation but I do have teen daughters one of whom has had a mild mh problem.
Blewbury65 and favouritecardigan you both sound like wonderfully supportive mothers but I imagine it is a fine line between giving support and enabling poor behaviour.
I think you probably need to be very clear in your own minds as to whether you are diving in to help in a crisis as a one off or are you enabling ongoing poor behaviour and self-created problems? If the latter, then obviously that needs to change.
If you are supporting them financially, then you do have some say over the ground rules and I think I would be drawing up some sort of mutual living agreement which they would have to agree to, in order to live at home. You could sit them down and have a discussion and give them a warning and say that you haven't been happy with the way your mutual living arrangements are working out, and from Easter onwards, if nothing has changed, then you are going to start imposing the following agreements over:
- mental health (having some sort of plan with regard to an assessment, therapy, perhaps even outside support, behaviour to support good mh like exercise)
- money (having to earn it and contribute towards rent and living costs, even if you save it up to give it back to them when they eventually move out)
- chores (you are living in the house as adults and the chores need to be split equally as this would be required in any other shared living arrangement)
- behaviour (they need to be respectful of you, your home and your working hours) If they are doing something that upsets you ask yourself "would I tolerate this behaviour from any other adult guest?".
All of this I know sounds quite prescriptive and difficult to impose when you have started out helping in a crisis but long term, I don't think you are doing them any favours by enabling them to have duvet days and be late for lectures. Certainly stop giving lifts and start upping the expectations of what they should do be doing in terms of contributing financially and doing household tasks. Presumably you have already contributed quite a bit of money to getting them established at their first university courses? So why should they not be contributing now? If there is no financial consequence for not succeeding, then surely they have little incentive to do well this time?
Also, if you help them too much, it gives the underlying message that you are not confident in their abilities to sort themselves out, which is the opposite message we should be broadcasting!
In the short term I imagine they will probably resent it rather when you start to impose certain boundaries but in the long term I think they will thank you for encouraging them to be resilient.
Good luck 