I commend you (and welcome you) for trying to create an accurate tree. The only way to do that is through using sources--some of which may not be on the Internet. When you have gathered your sources, you must then analyze them.
For example, could a man have six wives and 20 children? Yes, of course, he could. In past centuries most families, esp. in the Americas, lived on farms and needed big families. Many wives died in child birth or shortly thereafter, which necessitated remarriage.
But did this particular man have six wives and 20 children? That requires analysis of the sources and some logic. If the births of all the children are laid out, are there problems (children born several months apart, birth date of the child of one wife falling between to of another)? If so, multiple individuals may have been conflated. Was a man NOT Mormon and married to two living wives at the same time? Think conflation.
By laying out all the known facts from census, birth, death, marriage, and probate records (among others) and looking at the pattern(s), you can tease out some of these conflations.
I wouldn't worry too much about whether the name was recorded as Isaah, Isaiah, Isaia, etc. At a time when few were literate scribes wrote what they heard. I've even seen some cases where the same individual in the early 18th century signed his own name differently at different times.
Patterns are more important.