I also wonder if the twin thing has slowed mine down. They are just not motivated to do things like other babies as they have hot each other!
i got told off centred play was the most important, but like you found the physio a waste of time lol. Every time we would do it their was teArs all round. I made spent a lot of time trying to get them on their knees kneeling while playing too and had more success with this. In the end t2 started to crawl after hubby put her on all fours and pretty much forced her limbs into crawling motions. Obviously something just clicked. Still no luck with t1.
It's such a frustrating time, hang in there and hope you get right answers or reassurance from the pead. Keep me posted, I'd love yo know what he thinks.