We have been using a combination of Angora goats and pigs to clear land quite successfully for 4 years. Goats first, then pigs, followed by goats. It's slow, but extremely effective. They also will go after grubs and other harmful creatures. Throw in a bale of straw every once in a while for them to make beds with, dig into the ground, eat. You'll need to lime where they have been because they make the soil acid. When we have scrap sheetrock, we throw that in for them to play with and to sweeten the ground.
I wouldn't put pigs in with the goats. It's okay when the goats are large and the pigs are small, but that situation doesn't last for long. Ditto chickens. You will probably have to supplement their feed. They'll eat all of your scraps, except citrus. If you want to get rid of a tree and pull out most of its root system as well, keep "drilling"--wiggling sharp stick into hole by the roots when the ground is wet--and pour a little whole corn down the hole. They'll go after it.
We time our pigs so that the goats aren't kidding when pigs are there. The blood smell will excite them.
A couple or 3 pigs are some of the most effective investments you'll make. Great food, low cost. If you prepare correctly, they take up very little time each day.
Handle the pigs when small. Get them used to you. Scratch their heads. Have a special call for them you use every time you feed them (we just use "Pig pig pig."). Then when they're really big, they won't be as formidable. Do not name the pigs if you're going to eat them. Tell children that if the pigs start to talk, herd, or have complimentary words in spider webs written over them, you won't eat them. Otherwise...