I'd just give them time. My daughter started leaning to the side when sitting down then just gradually got into a crawling position over a few days. Then she worked out how to use her hands to push herself back to a sitting position 🙂
My eldest never sat from lying down, he used to roll into his front and push up to sitting that way. They just work it out themselves.
Definitely not failing they all go at their own time! And all of a sudden they’ll just get it and be off. My son went from only sitting to getting sat up from laying, to crawling all in the space of about 3 weeks (started crawling last week). Only thing I did was putting him in a side sitting position (like legs to one side) to encourage that action if that makes sense!
My baby is 8 months, she can't go from laying to sitting or crawl. Your not failing as a mum they will do it in their own time