Another potty learning ? - regressing and difference between home and out

[4Marmalade]

Help me out here.  My twins are 3 years, 3 months old.  It was maybe 6 months ago we started potty learning and it went well.  We switched straight to underwear and they started peeing on the toilet fairly consistently.  No poop though.  I figured we would just continue with the underwear and it would come with time.  Two months later I was still dealing with poopy underwear multiple times a day so we went back to a diaper for daytime.  They were a bit upset about losing their underwear but I told them once they started pooping on the toilet they could wear it again.  For about a month things were fine - still peeing on the toilet, totally dry all night, no accidents.  Still pooping in the diaper but at least easier to clean up.  For the past month I have been getting extremely frustrated as they are now peeing in the diaper again.  If they do pee I make them change themselves (with a little help from me with their clothes if needed) and put their diaper in the garbage.  The really annoying part is that when we are out of the house they have no problem peeing on the toilet.  We went camping for 3 days and they peed on strange toilets, outhouses, etc... but when we are home they mostly pee in the diaper.  What's with that?!?  I guess I can just switch back to underwear again but I really doubt they have made any great strides toward using the toilet to poop and I cannot imagine dealing with that mess again.  We have even tried a reward chart but they don't seem to care.  My older two learned at ages 2 and 2-1/2 and I always swore that I never had to do anything and they would figure it out on their own but now I'm second guessing myself.  Any ideas?