I know how you feel my little one didn't walk until after 18 months. Mine wouldn't use any of the push/pull toys nor would she cruise. I had her in PT for 2 1/2 months and I think it came down to will. She wasn't ready and didn't want to. It is so frustrating listening to all the comments you get both positive and negative. I remember them all.
The best advice and knowledge we learned from PT was working on up and down skills. Toys/games that build and strengthen the muscles in their legs. Find a toy or game that makes them bend/squat then stand back up. Picking a ball up off the ground and putting it in something up high. I think this really helped. Also don't let them sit in the W position with their legs behind them. This is bad on their hips and will effect growth eventually. Good Luck!