Well put @ScentOfAMemory.
Your SiL @Mommymoments is probably of the same thinking. You need to rise above it. When my children were in Reception-Y2 I wouldn’t have touched the PTA with a barge pole, much less cared what they think. However PTAs change and when my children were a little older a much more sensible group started running it. I couldn’t help noticing that they were parents with less time on their hands and a more professional approach. Not all PTAs are the same thankfully.
If they are the types to use their PTA gatherings to gossip and whinge then you can bet they’re doing it about lots of children and parents for various crimes; children being too clever, not clever enough, children winning all the prizes, children who never get a sniff of a prize, parents working full time, parents not doing enough, parents too involved, parents too poor, parents too flash etc etc etc. Leave them to it.
In my experience the superstars in prep or primary aren’t necessarily the same ones later on and no one ever got sacked as, for example, a partner at KPMG because the fact they only ever played a sheep in the nativity is uncovered. No of it matters.
I expect these parents will eventually emerge from the prep school bubble and have to start worrying not about why little Tarquinius had the glory snatched from him by the OP’s children when the glory was rightfully his on account of the Victoria Sandwich they baked, to having to worry about why Tarquinius has dropped out of 6th Form and started dealing.
ignore it.