Liamsmum - what a pain for you - the situation can be as easy or difficult as the people involved choose to make it, and FIL seems to be choosing the hard way. Luckily step MIL seems a bit more helpful - maybe she's even embarrassed about his behaviour, even if she hasn't said anything?, and perhaps she could be willing to help out?
Why not consider being honest about the lunch situation - I am quite open about the fact I hate cooking. I'll be a good hostess for a couple of days, but 5 weeks is stretching your hospitality a but far. Perhaps you could say that as you're cooking tea they could prepare lunch - or take you out to lunch? Or you could just say sorry, you can't face doing lunch (AGAIN) today, so .... (give them a chance to offer to make or treat you out) and if no such offer is coming, say you're going to treat yourself. Or why not arrange a zoo/park visit for the morning, which will incorporate a cafe -for-lunch visit? I've done all these things, and there's never been a problem (only when I've gone ahead and made the lunch without saying anything and got in a bad mood!)
Re the tv - is there a tv in your bedroom? I know you may feel like you shouldn't be evicted from your living room, but you can just look on it in a different way and think you're getting an hour or 2's peace and quiet. If FIL comments again, you could just say ypou're going to watch tv in your room if he's not enjoying it (nicely of course), then you get your peace, hopefully you'll look good, and he might think twice about being so rude. On the other hand, does he get to choose something he likes occasionally - when staying with my mum & step dad for the week, they didn't once let me watch something I wanted, and I was treated to non-stop cricket and war-documentaries the whole time, and bearing in mind I don't even have a TV, so it would have been a very rare treat for me, I was really p*d off by the end of the week, especially as I felt I had no choice byt to sit & suffer as I didn't want to appear rude by going off & shutting myself in my room all night. So that may be a consideration to help keep the peace?
I also have problems with noise, especially during nap times, so now I say I'm just going to put ds down for his nap, so if anyone wanmts something from upstairs, can they get it now, as I don't want anyone going up while he's sleeping - the stairs are so creaky - sorry etc. Then during nap time & make them stick to it. If they really need to go up, I offer to get the article for them, as I know I can do it quietly. We even fitted foam to our bathroom door frame, as FIL CANNOT shut the door quietly, and he always needs to pee at 3 am!
Finally, his comments on ds & the stones. What a pain - I'd be so annoyed by this. I suppose at times it wouldn't hurt to show you're annoyed? Maybe then he'll back off. Or you could sigh and say, well, if I didn't have to wait on you hand & foot I would be able to take better care of him! (Only joking). Maybe you could make a joke along the lines of how active and adventurous he is & what a shame you don't have eytes in the back of your head etc. You could also try asking him & mil to keep an eye on him - quote fil's keeness for him to be observed constantly, while you go off & do something (like drink the vodka). If all else fails, moan to dh, make sure dh witnesses the critisism & get him to politely ask fil not to make such comments.
Good luck!