Wisdom of buying an investment property 4 years before retirement

We are a dual income couple. Annual income of $400k.

We are considering purchasing a second property (an apartment in a nearby HCOL city ($350k) for our adult child & spouse (employed in a secure job) to live in and pay us rent. If we put $90k down, their monthly rent would pay for the mortgage and HOA payment.

We currently have $3.3 million in investment retirement accounts that we don’t want to touch; and $130,000 in a HYS account.

Is using $90,000 of our HYS a good idea to purchase an investment property? Or wouid we be better off paying off our current mortgage ($110,000 is left on that mortgage – $2,200 monthly payment- and the house is valued at $550k).

We are motivated to help family out but also make a sound investment. They plan to move to a larger place in 4 years so the timing might work out well; as long as there isn’t a hole we aren’t seeing in this plan.