Can I take online courses to make up for poor past community college performance when applying to a four year college?
My advice would be to go to the website of the university you are thinking about enrolling in, find out who the course coordinator is, and email them about your situation.  Explain that you are willing to put in the effort to get your knowledge up to an acceptable level.  You may find that they can offer you a bridging course, or suggest having sessions with a personal tutor like you are planning.

I found myself as tutoring a mature-age student who was very much in a situation similar to what you described.  The course coordinator emailed the maths academics to see if anyone was interested in some private one-on-one tutoring, and I took up the offer.  Ultimately, the student opted to drop out due to the feeling of being overwhelmed with the content (and they were struggling greatly to understand basic high-school level concepts), but the fact is the university attempted give the student every possible chance of getting in. There is nothing to lose by trying.