How many legal guardians can a elderly or parent have in the state of Hawaii?

I presume you mean by legal guardian a kind of "tutor" and this person to be responsible for the well being of the elderly parent, and to take care that his/her income money is spent in a normal way and no money is disappearing, so that lots of difficulties would arise with the heritage. Here in Belgium / Europe, there is only ONE. More than one is looking for trouble even before you commence.

Generally it's only one, however I've seen co-guardians but they don't seem to work very well.

only one at a time.

Wouldn't make any sense to have more than one in force at same time , because then one could end up un-doing something the other had just done, or otherwise messing up the plans one had already laid. Guardian is just a state -appointed POA, and same general advice also applies to POA. in very rare instances does a dual- or triple- headed POA work out. Agencies and facilities only want to deal with ONE person, similar to a Landlord, they only want to have 1 person on lease, it keeps things easier all around.

I wouldn't want more than one. Too many people involved. You may be able to have a secondary named in case you can't handle their stuff.