@IsHeAnal I don't understand why it has got to this level, the first time he "told tales" he should have been told to mind his own business, they are your children and you will parent them how you choose.
His actions are really creepy, his little "tests" is he testing who you love more by making you reprimand your girls on his say so?
Regardless of what he does for them or buys them this behaviour is not acceptable. He is not being supportive, he is undermining you, every time you give your girls a row because of his snitching you show the girls you are putting him above them. Your argument is with him, not them.
As for them sharing a bed and whispering in the evening, are you happy that they do that? If so his opinion doesn't matter, he can like it or lump it.
I don't think you are a lax parent, surely everyone needs time out just now and structure and routine relaxed a little, so much has changed for your girls in a short time, they have met your new partner, got back in touch with their dad, new partner moved in to their home, their relationship with you has changed, it's no longer just you and them, schools closed and activities stopped, their only constant in all of this is each other and if they want to spend nights together chatting what is the problem? They need down time, chats to process their day, they don't have their school friends to talk through their worries or thoughts each day.
You clearly had concerns things weren't right or you wouldn't have posted, don't ignore that niggle, there may not be sinister motives behind his behaviour but you know it isn't normal and lots of posters on here have shared their experiences and thoughts. You need to weigh up all the points and, if that niggle is still there, do something about it.