In two of the Kingdom Parables, my study Bible’s interpretation differs from yours. With the Parable of the mustard Seed, it says says the ‘birds’ do not represent evil as they did in the previous Parable of the Sower. It goes on to say that the large growth of the mustard tree is good and represents the huge growth of the Kingdom from such a small beginning. In the parable of the Yeast, it again negates the yeast as symbolizing something evil; but rather its dynamic growth character. Again, pointing out the spread of yeast in dough, parallels the future fast growth of the Kingdom of God by the inner dynamic of the Holy Spirit. Could you give further explanations for your unique interpretation of these parables?
The principle of expositional constancy holds that when things are used symbolically or allegorically in Scripture they tend to represent the same thing everywhere. For example, leaven is consistently used to symbolize sin. (In 1 Cor. 5:6 and Gal. 5:9 Paul used yeast in its normal symbolic sense to show how boasting and false teaching can quickly work through the whole church.)
When interpreting the Kingdom Parables, many theologians violate this principle to avoid having to conclude that the Lord was saying there will be sin in the Church and that ministers of Satan dwell therein as well. (In 2 Cor. 11:13 Paul also said that ministers of Satan are false apostles who masquerade as ministers of righteousness).
Also their conclusion that the Church has become great although from humble beginnings is only true in terms of size. Both Paul and Jesus said at the end of the age large parts of the Church will become apostate and the true Church would decline in both size and influence (1 Tim .4:1-2, 2 Tim 4:3-4, Rev. 3:8, Rev. 3:15-17). We’re currently living through the fulfillment of these prophecies.
By the way, this interpretation is not unique with me. Many non-establishment theologians have interpreted these parables the same way. That’s how I learned it. Conduct your own study and see what you conclude.