Since you have the discus and angels and really no other tank either fish can live in (no, the 30 gal will not work for either fish), you pretty much have to live with the situation. Discus can tolerate 82 F but it is rather low; low temps tend to allow illness to develop for that species. Sooner or later, the angels will get aggressive towards each other if they are not a true pair. The discus may do the same.
You should consider finding a home for the angels (some stores will take them) and stick with the discus than a few further points; the discus do best in the 86 - 88 F range (the higher end works best.)
Even with a planted tank water changes are best for both the discus and angels - so, what are the size and number of your water changes. Also, what are your average nitrates?