My ILs live in the south island so usually visit for a week at a time. I usually get really stressed out as they do things so differently to me and it drives me nuts. I have finally, after about 14yrs

, learnt to relax and not worry about things that don't matter too much like cups being left in the sink etc. So that would be my advice, try and relax, plus I am sure they don't need waiting on
Also maybe you could go to them every 2nd visit, you could head there during baby's first nap and head home after dinner. That way you can get there and back in a day and not have them to stay