I assume this was during the early 1800s. Whether or not it was reasonable really depends on the point of view you look from. No slavery, must become a Mexican citizen, must learn Spanish, must convert to Catholicism.
From the perspective of the American settlers, the various rules and demands were too much. They had such a long history of self-governing that the idea that they had to have permission from someone else far away to do things seemed extremely foreign and rather ridiculous. They had come to Texas looking to farm or create a cattle ranch. They didn't understand why that meant that they needed to become citizens. Even more, why convert? Many had long been skeptical of Catholics.
From the Mexican perspective, they were trying to get the immigrants to assimilate into the society that was established. When you move to a new country that you intend to stay in, why not become a citizen. This would give you more opportunities and show your commitment to the new nation you want to call home. Spanish was the predominate and official language of the country. To do any official business it had to be done in Spanish. Slavery had long been outlawed so it was illegal to continue the practice. This is the new country that you willingly came to, you should follow the rules established. This nation said a national/state religion, Catholicism. It was the only recognized religion. If you chose to "quietly" worship in different way, but they didn't want people coming in and degrading a religion, belief system that they knew nothing about, simply because it was different.
