I wonder what type of lavender you'd purchased. I've lavenders munstead which are not suitable for topiaries, but the spanish lavenders are suitable. I suspect it might be the spanish variety. Why don't you just allow it to flower and trim it when it has stopped blooming. No need to worry about that it will go out of shape. Once you'd pruned it, it will get back to shape. Enjoy it's blooms and fragrance.

As for the jasmine vine. Nip off the tip of it leading vine. That usually stops the growth that particular 'stem' and forces side branches to grow.

Ianna