@Stunnershaz I’m so sorry you’ve had the shock of finding out such deceit.
While the fake account has helped confirm your instinct was correct, I wouldn’t keep responding on there. If he found out, he could report you (for using someone else’s photo). If you must send a friend to spy if he arrives for a meet up, for goodness sake make sure they don’t let him see them.
Get advice from Women’s Aid but adding my voice to others here, that if you feel safe (because he doesn’t know you know or are planning to leave) it may be best to stay there until you’ve sought legal advice, gathered all the information you can on his finances and weighed up your opinions. I believe teens under 18 get to choose which parent they live with and how often they see the other parent. So, be aware that if you move out, there’s a risk the kids may prefer to stay in their home (i.e. with their dad). Better to stay until you’ve figured out your best option. You may be able to remain in your home with your kids. But only stay if you feel safe.
Feigning illness is a good way to disguise your shock and hurt. Say you feel like you’re getting the flu and you have sore eyes (in case he notices if you’ve been crying). Lots of viruses going around right now last a few weeks, so may help you get through Xmas. Don’t have a drink if it might lead to you blurting it out to him.
Again, get advice from Women’s Aid. But for safety reasons, while you remain in the same house, be very careful who you tell if they know him. If you tell your mum, are you 100% sure she won’t get funny with him, blurt something out to him or tell someone who might tell someone else who knows him? If she might, just tell your mum you’re not happy with him, rather than the entire story.
If you’re not great with technology and he pays for your phone, ask someone tech savvy for advice (hopefully someone on here) on whether he can check your location, search history etc. Do you have security cameras in the house? I strongly advise setting up a new bank account for yourself if you don’t have one and getting a new phone if he pays the bill on your current one, both registered to your mum’s address for now perhaps.
Much better to make a planned move. But if you feel at all unsafe, listen to your instinct and leave immediately. So have an emergency bag packed and with your mum/a friend (with your important documents etc if he won’t notice them missing). Good luck!