Hi,
I just came from a home inspection for a new home and it revealed that not only are both 40gal water tanks on their legs but the boiler is from 1989 and in rough shape. We're thinking of going tankless as this is a vacation property to usage is low. However, I'm confused about the components of the system.

Would going tankless allows us to get rid of the boiler or do we need to replace that as well?

It's forced hot air heat and our other house it forced hot water so I'm just wondering if the boiler only heats the water or also plays a role in the HVAC system. Thanks

If your boiler is furnishing the hot water for the heating system, then no, a tankless hot water heater will not replace it. The tankless hot water heater will replace the hot water tanks for use in the home water supply.

A issue you may have with tankless, for the water system, could be the piping. The systems need good water volume and flow. If your pipes are badly clogged, they may not allow for enough flow for the unit to properly work. I use tankless in my house, and just replaced it (I think the old could have been fixed, but my wife wanted a new one).

If the new purchase has forced air heat coming out of vents in the floor, it doesn't have a boiler, it has a furnace that heats air, not water.
Furnaces (and boilers) get smaller and smaller and more efficient as the technology gets better.

Two 40 gal hot water heaters were probably for big groups of people on vacation?
It might be cheaper and most effective to replace one only. When you aren't there, you just turn it off.
There are other issues with tankless besides the minimum flow to activate the heating element. It can get expensive.