Using present progressive with to omoimasu?

Hi everyone, I'm still a beginner (teaching myself from the 1st Genki book) and I'm a bit confused as to how to conjugate present progressive verbs like けっこんしています、はいています、きていますwhen using them with とおもいます (or to といっていました). Can't seem to find info on the rules for this.

For example, how do I say "I think Yamada-sensei is not married"? (dunno how to say it in the affirmative either)

Is this correct? 山田先生はけっこんしてないとおもいます (I think this is what I heard in one of the answers from the CD??). Because wouldn't 山田先生はけっこんしないとおもいますmean "I think Yamada-sensei is not going to get married"?

Use the dictionary form (plain form).

けっこんしていると思います
けっこんしていないと思います

sorry, what is "dictionary (plain form)"? Do you mean the plain form of the dictionary form/infinitive? Because I thought けっこんするwas the dictionary form. But still helpful, thanks! I can see something happening with 'て + いる' so I think I get it (hopefully). Just to check my comprehension, are these correct?

I think Takeshi is (not) holding a bag. たけしさんはかばんをもっているとおもいます。/ たけしさんはかばんをもっていないとおもいます。
I think Takeshi is (not) sleeping right now. たけしさんは今ねているとおもいます。/ たけしさんは今ねていないとおもいます。

You got it.