What report do I use if I want to see all activities from people in specific accounts?

Email performance, LP performance & Company web activity report will give you EM/pages information.

But if you want to see 360 degree view (sales notes, opp, EM, pages etc.), you need database and visualization tool like Hadoop/ Tableau.

OR you can manually create an excel dashboard with web pages browsed, email engaegment, keywords searched, Videos watched, PDFs downloaded, forms filled etc.

You need to specify what "any activity" is ... e.g. email sends, deliveries, opens, clicks, web page visits, form fills etc...

Then, because the capture for each activity or groups of activities are different, you'll have to go into the individual report types to fetch the data for the 10 specific companies.

Lastly, you'll need to do some work to make the data presentable, including stitching together the disparate reports into one

RCE can give you company aggregated email stats. If you want individual names, click+drag 'Full Name' into Rows under Company Name:

web page activity report with smart list filtering company name can give you pages viewed by leads from those companies

(the exported output isn't great, you'll need to do some editing in excel to aggregate number of page views by account)

As for form fills, I'd just use a smart list