Sil gets -
Free childcare several days a week plus odd weekends
Cleaner (mil)
Gardener (fil)
Free dog sitter Mon-Fri
Holiday home one week a year plus several weekends
Dh gets -
Holiday home one week a year oct/feb half term only
Occasional overnight stay for dd maybe once every few months.
Sil does live in same town we live 20 mile away
Are you kidding? Obviously your SIL gets more of this - she lives down the road! You're 20 miles away! Do you expect them to travel to you to provide child care to?
You've not said the age of your DD but presumably they get child care "several times a week" because their child is 1 and so doesn't go to school so they need the childcare to work and are down the road so it's easy for them, same goes for the dog.
You say odd weekends but you also get odd weekends - that's more child care than a lot of people get from their parents or in-laws.
You're trying to make your list sound worse when it isn't, phrasing it as SIL getting "holiday home one week a year and several weekends" whereas you get "one week term time only" - term time only has just started this year, don't forget the years they gave you it at peak time, for free. You also could have weekends - it's you and your DH that can't do it because of your shifts at work.
You're trying to be petty and make it out as if they favour your SIL when from everything you've said, it's simply that they live closer so it's more practical. If you want more help - why not move to the same area? Presumably you don't want that, you want them to accommodate you?
You sound like a child "but she gets this so we should too"