Having been through this myself but to nowhere near the extent you have, it is true that a dignified front has to be kept. It is unfortunate and the human condition in fact that we want what we can't have - to be frank, if you are really honest there was an imbalance somewhere in your dynamic between the two of you.
I can guarantee that in time he will realise he has made a massive mistake; unfortunately because of biology the way to go forward is almost impossible - thanks to the hormones raging inside of us women the fact that he is the father of your children means that this is a 1000% more difficult for you to walk away from and begin healing. However. I had wake up to the fact that co dependency is not healthy. It sounds like you are back here but with no friends / family to lean on. Any hysterics / emotional 'episodes' will be seen as such, and used as reasons why the relationship may have broken down in the first place. Unfairly, but true.
So, practically?
Right now you have to survive. Make sure you eat, and if you can't eat often make sure you eat healthily when you do - its not your body that did this so punishing it is not fair on it, especially if you are breast feeding.
Definitely get as much legal advice s you can.
Have a chat with the in laws, again NO emotion - they sound rather uptight and they definitely don't talk about feelings etc which is partly how you have ended up in this situ via your husband in the first place. Tell them that you have the impression from their behaviour that they seemingly condone your ex's behaviour. Tell them that you need time for yourself (do not say to heal or anything like that, it just gives them / him more power). Work out a timetable to be strictly adhered to for them visiting / having the grandchildren. They evidently have their own familial issues but that's none of your business xx
Selling the house is a massive upheaval especially on this terrible market. If you rent you can take as much / little of the furniture with you and make a completely fresh start; see it as 'practising' your new life. Then when the market improves and all the legal stuff is done you'll be far more protected, confident, and hopefully well off. Otherwise if you want something more immediate, house swaps are awesome too - you need to get out of there ASAP. If you love the house you may be selling something that in the future could come to signify something good, not just the bad. A change of decor, furniture, even the layout of the house - you need to be in different surroundings for a while just to heal a little.
Do go to the doctor and ask to be referred for therapy. You don't need anti depressants, youve been through a massive trauma and you're grieving. But you do need somebody objective, and to be perfectly honest somebody who won't sit there and agree with everything you say. I was emotionally abused very severely, but even I had to stand up and accept the fact that in some way I allowed it to happen.
Make time for yourself - google everything you can from mum and baby swimming sessions to toddler groups, anything that will give your days structure and a reason for you to get out if the house. Most importantly pamper yourself. A hot bath, joining a gym, making the most of jacuzzi, sauna etc - really helped me. If you can get babysitting favours off family etc. they are there to support us in times of emergency - this id an emergency!!!!
Your husband is a wally. You think you want him back but you don't - you want the old him back, not the person he has become. And people do change unfortunately - if I remember who I was 16 years it's a world away from who I am now.
When he skypes the little girl, look amazing, be friendly, amiable, but give nothing away - if he asks you any questions be smiling and gracious but give short answers. If he notices the difference in you (which he will, trust me) apologise and say that your life is private now, and that you are happier. And. say that is all he needs to know. You see he's 1000s of miles away sitting there with this girl thinking you're safely at home an emotional wreck pining for him; that means he doesn't have to worry about other men being on the scene which believe me, if he even had an inkling of a thought otherwise, he'd be concerned. Very concerned.
Lastly remember, you are doing all of this for you sbd your children. NOT him / to get him back. This will be a life changing experience, and do it should be. But if you embrace it as the beginning of a new, independent adventure for you and your babbies, therein lies the light at the end of the tunnel.
Good luck sweetie x