Hello and thanks for your question.
You have every right to be cautious, both in view of what happened in the past (and therefore your fears about whether your ex would lose his temper with the girls, or with you over the contact arrangements -which would affect them too - or more generally, just the fact that he has not seen them for so long, and a) what would the effect be on them of introducing a virtual stranger into their lives, and also b) what is the level of his commitment, and whether he would start seeing the girls, then stop, and thereby upset them by losing contact with them again.
The other side of the picture is that in principle it is a good thing for children to have a relationship with their father - and it is government policy that children should have contact with the parent that they do not live with, unless there is very good reason why not.
However, each case must be decided on its merits and accroding to what is in the best interests of the children.
You need to consider:
Whether it would be good for the children to have any contact at all with their father? If not face--to-face, then by telehone? email? skype? or face-to-face? If yes, how often? where? for how long each time? on his own? if yes, should he have them overnight? if yes, have you seen his accommodation? is it suitable? or should his contact with the girls be supervised? if so, by whom? Should the contact be at a contact centre?
I would strongly advise you to get some face-to-face legal advice - here's where to find a specialist family law solicitor:
You caan negotiate either between the two of you or via solicitors' correspondence or via mediation, or as a last resort apply to court for a defined child arrangements order (what used to be called a contact order).
But the family court now requires the parties to have attempted mediation before it will consider an application for a court order.
Here's where to find a family law mediation service:
If mediation breaks down, then you can apply for a defined child arrangements order on form C100. Here's the link:-
I hope this helps and I wish you the best of luck.
Thanks and best wishes...