There's the typical Roth IRA or Traditional IRA (post-tax vs pre-tax contributions).

That said you may consider a Solo 401k to contribute 10x more than an IRA annually if there's self employment robust enough and no employees. $50k might be enough to do some PMLs but probably not for the IRA/401k to actually own real estate.

Quote from @Maya Jones: This type of thing is like trash companies, you will hear it right away from your tenants if their car is blocked in by snow.

Once they earn income open Roth IRAs for tax-free growth.

That’s a big hit before you even invest in real estate.If you really want to move retirement funds into real estate, look into a self-directed IRA or solo 401(k) instead.

Could you please recommend a company to take a look at it?

Denver is a great market and there are also several great PM companies here, just sayin! 

There are a lot of things that need to address for a PM company between compliance with the state, local rent control in a lot of your area you'll be covering, a lot of competition that is in your area, marketing/ads, and so much more. 

They seem like a rock solid company.

@Megan McclungNon-recourse lendersA Solo 401k is better than an IRA for investing in real estate with leverage since the 401k is exempt from UBIT on leveraged real estate unlike an SDIRA.