He "returned your call" when you didn't leave a message. He's been waiting for contact, and jumped on it. He was being all cool, not answering, letting it go to vmail. But then you didn't leave a message, so he had to call. And then when you didn't need anything, he tried to prolong the contact, and then leave matters unsettled so you'd need to call back. Don't.
Your H said he was "thinking about" having them this weekend. Well, it's Friday afternoon and he needs to have planned it out a little better than that.
Your response was that you would "think about it" too. That's not telling him no. And you have been thinking about it, and you've decided that an overnight for S2 might be ok but not for the baby.
OK. But don't tell him that. Wait and see if he makes any concrete plans. He won't. But if he does, then don't tell him he can't see his kids, ask him what his plans are. If it involves an overnight for both, ask him: "How do you plan to feed the baby?"
If you tell him he can't have them overnight, he will either demand to, or more likely use that as an excuse not to see them at all ("you're so controlling!!"). If you let him figure it out, he will realize that he doesn't want to deal with a nursing 5mo old overnight without her mommy.
Right now you are tempted to call him and say, "Its Friday, are you taking the kids or not?" But don't. Obviously if he was going to, he would have told you by now. He may call tonight or tomorrow and try to figure something out for Saturday night or just for a few hours. Or not at all. Go on about your weekend as if you won't hear from him, and be pleasantly surprised if he does arrange something with the kids.
