I doubt that there is a complete English translation of "Having the Three Convictions" by Tsongkhapa available, but I don't know for sure.
Lotsawa House is an organization which does a lot of translations from Tibetan into English. They have a facebook page. Perhaps they could give you more info.http://www.lotsawahouse.org/index.htmlhttp://www.facebook.com/pages/Lotsawa-House/12473129263
Are you practicing under the guidance of a Lama? If not, then reading the details of all this stuff may not be so helpful over the long run. Tsongkhapa's other teachings are great as well.