6-month checkup, Nikolas opens all doors, potty training

Six-month doctor's checkup and vaccines:

Michael
height: 25 1/4" (10-5%)
weight: 13lb (5%)

Sonja
height: 25 3/4" (50-75%)
weight: 14lb 7oz (25-50%)

Now that our nanny, teta Divna, is gone back home, and Robb is on a 2-week business trip, we are going through a major adjustment period. Nikolas still uses her phrase 'Sutra lane kada svane' which basically means 'Never' when asked 'When will you be a good boy?' He doesn't yell as he used to when she was here. I thought this was the case, he was just asking for attention when she and I talked without including him, and when he reached his limit he would screech in high pitch voice, hit, throw things, and everything else he is not supposed to do on purpose. Now that it's just me and him talking to each other, he is much more controlled. He still likes to poke Sonja and Michael though. By Murphy's Law, as soon as I was alone in the house with the kids, Nikolas learned how to turn the knob on the door and get out of his room first thing in the morning. He would then immediately go into the babies' room, stick his hand between the cribs' rods and touch their faces. He likes to go for eyes, of course, as kids usually do... Once he got the babies to fuss or cry, he would then go through the kitchen (there is no point having that child gate to the kitchen anymore!), and into our bedroom and excitedly climb on the bed and jump around. I have no idea what we did with the kid-proofing stuff to prevent him from opening the doors , so now I have to wait for 2 weeks until Robb gets back from his trip to help me find it.
Even when the babies are in their Exersaucers or on the floor Nikolas loves to run over to them and hug them first (he completely leans on them, presses them with all of his weight and sometimes steps on their hands if we are not right there to stop him), and then he'll start sticking his fingers all over their faces, particularly eyes and ears, and sometimes when they are in the Exersaucers, he'll push their heads back. I have to police him around babies all the time. Still, it's obvious he loves them, especially Sonja, and she adores him while Michael is a bit more wary.
We haven't progressed with potty training, other than that Nikolas now empties his potty into the toilet by himself and flushes. He still pees in his shorts if I don't put a diaper on him when I take him outside. We normally spend a couple of hours in front of the house while the babies nap (almost 9am-12pm) where he plays with his tricycle, car, etc. and we also walk to the pond where he still loves to throw mulch in the water. At the end of the play he'll push his transport into the garage and park it extremely neatly; he does this with his little toy cars and truck inside too--he obviously enjoys sorting and arranging things. Chances are good that he'll grow into a neat guy :)