1. Given that I would be trading up I would like to convert two or more older homes to one. Is this possible if there are different buyers for the homes? What if there is excess cash from the sales?
1. Yes, it possible to sell two homes as the relinquishing properties to different buyers and have a single replacement property. However, the clock starts ticking for the 45/180 days on the closing day of the first property. Depending on the markets you are buying and selling in, that may be challenging. If there is excess cash called a "cash boot" in 1031 terminology, you will pay taxes on that.
2. What if I take back a loan on an exchange? Again, what if the total sale price(s) wind up being more than the new purchase?
2. I'm not sure what you mean by "take back". However, a requirement of a tax free 1031 is that the loan on the replacement property is equal to or greater than the relinquishing properties. If there is less debt on the replacement property, there is a "debt reduction boot" and tax will be due on the difference.