Spiny eels are "difficult" because people treat them like ordinary community fish, which they're not.
They're sensitive to bacterial infections, the prime cause of which is skin damage. So you should keep small species at least in tanks with sand, never gravel.
Although they're not always found in brackish water, keeping many species in slightly brackish water does seem to help (it helps if you research this aspect before buying, as only some species are brackish water tolerant).
They're difficult to feed because they lose out if forced to compete with loaches and catfish, so they should always be kept as the only nocturnal, bottom-dwelling fish. They do need fattening up immediately after purchase, as the chances are they haven't eaten for weeks. Worms, especially earthworms, are ideal.
Macrognathus spp. are at least somewhat social, so keeping them in groups will help. Mastacembelus spp. are territorial and potentially aggressive to one another, so again, do your research here.
They jump out: keep the tank covered, and where possible install floating plants (real or plastic).
Cheers, Neale