Bitter Yuck worked for Roxy. It's really nasty tasting. Bitter Apple works for other dogs better. Some dogs bite/chew regardless. They are worth a try though. We had a few wire areas blocked off, she was restricted to only 3 rooms for quite a long time. Now she is fine regardless of what room she is in... but she follows us from room to room, so it's easy to keep an eye on her.
One thing I started doing with my hands was to make a fist, leaving no fingers open to grab onto, and just hold my fist in front of her face. It would make her so mad! I guess I wasn't playing fair.
She would get so frustrated, she'd start grabbing at my clothes. It's going to be awhile before this phase passes, so get used to watching them constantly, saying 'ah ah', 'no bite' yelping, 'leave it', 'drop it' over and over and over... however long it takes.
Collars/harnesses/leashes... just keep trying. These are not natural to puppies, and they have to learn to accept them. Leave them on awhile, remove them, then back on awhile. They will gradually get used to them. It's a learning process. Be sure to reward all successes with praise & tiny treats. Good luck w/your little ones.