Strange question I know but I'm not a mother and am worried about a friends baby. How much liquids on average should ten month old be drinking every day. I know every child's different but just an average from your own experience maybe?

A rough guide is about 20 ounces or so... if he is also taking in a decent amount of solids. This will sometimes vary from day to day... once in awhile a bit more, sometimes a bit less.
If he is not having much solid foods yet, then he will need to have more formula.

What about other things like where should the average ten month old be as in sitting/crawling standing etc and what about interaction? Like a guide to where his development should be... thanks x

It will be somewhat individual, but here is one guide. Keep in mind, some babies will master certain skills a bit earlier or later than others and it can still be perfectly fine. For example, you will get some 9 month old babies starting to walk, while others won't take off until around 15 months... majority will be somewhere in the middle.

First Year of Development: American Pregnancy Association (http://www.americanpregnancy.org/firstyearoflife/firstyeardevelopment.html)