Wanting to help some feral/stray cats nearby, not sure how to? Trying to make them inside cat/s.

So we already have a dog and a cat (both are very chill, and are almost/are seniors) we've noticed 3 cats (mama cat and 2 babies, that are old enough to be eating the cat food we put out, and they at least appear mostly healthy) consistently by our house, as we've been leaving cat food out for them.

They're still rather skittish, but they let us get surprisingly close (around 3ft-ish at closest) however we haven't been able to get close enough to pet any of them. We (the whole house) would like to adopt them, however we have concerns about how to manage that.

We luckily have a free room that is empty 99% of the year, so we have a place we could put them where we could put all the stuff for them, to help them acclimate to the space and allow the other furry family members & them to get used to each other's smell.

However, we've never done something like this before, we have some (very little) experience with outside cats becoming friendly, but not with bringing any inside. Especially not when we already have other furry family members.

Luckily there is already a way we have set up to get them spayed/neutered, & vaccinated, I just need to know, is this even a good idea? I don't like to have random outside cats roaming the neighborhood, due to how awful they are for the local ecosystem and bc I know they aren't living their best and safest life outside.

I'm just wondering if anyone else has experience bringing outside cats (stray/feral) cats inside and getting them accustomed to being an inside cat? What are some stuff I should keep in mind? How can I make this easier for everyone? Could I be in way over my head?

I don't want to do anything until I am fully ready to take them in, if that's what we choose to do.