Share iCloud calendar with Google Calendar

Ok, so I'v moved all my contacts, email and calendars to iCloud and everything is wonderfull.

I share a few calendars with my girlfriend and she is sharing her study calendar with me.

We have a shared calendar set up, where we enter when our son is in daycare and we have another shared calendar with things we do together.

Now comes the tricky question:

How do we share our icloud calendar showing our sons day in the daycare, with our parents who don't have any Apple devices and only uses google calendar?

Reason for this is, we live in the same city, and sometimes they want to go and pick up our son. With a shared calendar like that, they would just be able to write a note in their synced google calendar saying that they are going to pick up our son, and we would see it in our synced icloud calendar.

Also, my girlfriend only have an old-school cellphone. She is now finnaly getting a smartphone through her work.

Only problem I see comming with this, is that her phone is not going to be an iPhone.

So how do we keep sharing all our icloud calendars with her on a windows phone 7.5?

Is the Apple ecosystem finaly getting so clamped up, that it won't allow users who happen to have frinds or family without i-products, to share their life with them?

As everything stands now, I'm getting the feeling that Apple demands me to buy Apple products to all my family and frinds, just so that we can still interact and plan our different lives through shared calendars on icloud.

Can this really be right?

I hope I'm just missing something. Cause I really thought, that icloud would be this outstanding product which would make my cloud-life the easiest thing in the world. Instead, it really seems to be a step back, in the cloud evolution.