I do feel for you! My own mother just let me get on with it and never said anything. Mil, sil and bilsgf however were and still are of the opinion that I starved both my boys by only giving them milk until 6 months.
It was really hard at the time with all their comments, especially as sil had her first baby 2 months before I did and was doing everything 'right'. ie jars of baby food at 16 weeks. A year after I had ds2, bilsgf had her 2nd child after a 10 year gap and of course did everything the same as she did for her first - baby rice at 14 weeks, because thats what she knows.
You have to remember that its just one stage of baby's life and will soon be over. Stick to your guns.
You also have to remember that sooo many women had babies and were told to wean from 16 weeks and that solids would help them sleep through etc etc. Try to think forward 25 years and some dil of yours saying that everything you did with your baby was wrong. Thats how your mil feels.
However, when sils pfb was 2, there was some conversation about what a sicky baby she had been (projectile vomiting up the contents of her jars most meals). Mil looked all thoughtful and said 'your ds1 wasn't sick ever was he?' so maybe its sunk in slowly!
Its very noticeable now when family get together that our two boys are bigger and eat absolutely everything so I think the proof of the eating is in our little puddings!