Is using two tos next to each other in a sentence ok?

The sentence is just fine as it is.

I am going to drink two 40 oz. beers. I will have two too.

It's grammatically acceptable, but you've chosen an awkward and clumsy way of demonstrating what you mean. If you DO use that sentence, yes, inserting a comma between the two "to"s will make it easier for the reader or listener to understand.

You do not have to correct it as it is perfectly grammatical. In fact the rules of English grammar are the very reason why the two tos occur in the first place. It should also be noted that they are two entirely different tos, each serving a different purpose.

You could say "needed to in order to get them to stop" but the others are right that the whole sentence is stylistically flawed. Simplify. 

It's correct, and you don't need a comma, but it's a bit clumsy. If this was in casual speech, it's fine, but if it's in writing I'd find another way to say it. I suggest 'as long as necessary to get them to stop'.

I'm with Caroline. While it's technically correct, it's an ungainly read. Rewrite to eliminate the double word.

A good rule of thumb when writing is to consider the reader and make your writing flow as well as possible. In your example, yes it's acceptable to write as you did, but is it the best and clearest way of expressing that thought? Will the reader get tripped up by all of those prepositions? (There are several...).

My suggestion is to rewrite it to something like: They allowed it to continue as long as it had to; it was the only way to get them to stop.