It's a T5, not a T1, and you could be in a load of trouble.
I don't know why you changed your mind, and it's none of my business as you are not my client, but I do know that a lot of people use N12's when they have no intention to move in, and then find out the trouble they could be in and so they change their mind. In your case, the tenants agreed to move almost immediately after the notice was served, making your predicament especially dangerous.
If you are not going to move in, I would provide them with a letter, in their hand for speed, and then by registered mail, explaining to them your life-change that precipitated you having to withdraw the notice, and advising them that:
You are withdrawing the N12 notice
You will not be relying on the notice and will not be filing an application to the Board
Your a little dramatic and threatening for my taste / predicament dangerous good grief
tone down your drama
That if they wish to leave without notice, that you will grant them permission to do that by signing an N11 agreement, but with the understanding that they do not have to leave and that you will not be moving in.
Offering to pay any costs they have had by your change of heart (hopefully nothing to this point).
If your reason is phony, and if the notice was crap, it may not save you, but if you legitimately had a change of circumstances, income, job loss, job gain, birth in family, death in family, change in financial situation etc., then you should be protected from a claim by the tenants.
I FIND YOUR RESPONSE A LITTLE DRAMATIC AND PRO TENANTS
predicament dangerous phoney
he filed the notice in good faith and yes things change
he just need to send a note by registered letter and one delivered in the mailbox to cover himself
no offer of money good grief
dont mention any reason