Hi Op
I can see two sides to this situation
Obviously its up to mother in law what she does her husband who has passed away Coat.
Op
I don't think you are being petty,(I think you may be a bit envious,fed up,with the Blatant favoritism Shown by MIL towards SIL, (which is hardly susprising/understandable so.
You are human after all.
Easy for some Posters to be judgemental,as totally far removed it, but if it was happening to either of them, I bet few/some of them,would feel different about their view points.
Some/few of Posters are hyprocites
Money isnt everything,Rise above it ,don't let Showy,materlistic shallow mother/sister in Law irritate/ get under your skin so much..
Does mother in Law help you in other ways such as practical way for e.g baby sitting or etc then?.
Op
I also think some of the Posters here, come from middle class/ very money posh backgrounds so being giving such massive amount of money by a family member/having hand me downs costing a few hundred,seems quite normal to them.
They take it for granted,where as a lot of people have to borrow a loan from bank,scrimp/save etc,to acquire that sort of amount of money (500k).
So reading btwn lines reaction wise from some Posters they see your viewpoint as a attack,negative reaction on their kind of life style choices /upbringing possible..