There is no difference. The only difference is that different parts of China prefer one or the other. You should also be aware that you don't have to use both parts. For example, you can say "要是X," "要是X的话," "如果X," and "如果X的话" with little change in meaning! The most confusing part about learning Chinese is learning all the many ways to say the same thing!

They are similar but have a little difference...”要是“ something like Subjunctive Mood and with strong willing. 如果normally we use it as "if " in English. ”的话“ can also be changed to "呢？" example 1: a. 如果你不去的话，我们就不等你了。b. 要是你不去的话，我们就不等你了。（same meaning）(的话can be omitted in this sentence & 呢can also use as a replacement) example 2 : a. 如果你不吃饭的话就不会长高。(just tell the kid) b. 要是你不吃饭的话就不会长高。（with strong feeling）(的话can be omitted in this sentence & 呢can also use as a replacement)

There is little difference between them,they are assumed clouses.but the latter is more offical.

same

There is no difference in meaning between them. The subtle difference is that "要是" is uncommon in formal writing/speech while "如果" can be used in either formal or informal writing/speech. What's more, "的话" is uncommon in formal writing, too.