Self-employed, single-member LLC owner here. I have a SEP IRA. It lets my employer (me) contribute up to 20% of self-employed income per year + an annual employee (also me) contribution of whatever the traditional IRA limit is... $5,500 currently.
So if my net income is $100,000, I can make an employer contribution of $20K and an individual contribution of $5.5K for a total of $25,500 in tax-deductible annual contributions.
I'm not sure how the arrangement changes for a dual-owner LLC that may or may not have official employees on an actual payroll. Others can weigh in on that. Regardless, the SEP IRA is probably going to be a better arrangement than just a ROTH and/or individual traditional IRAs. That's just the investment vehicle I happen to know about. There might be others that are more advantageous for your situation.