Is Schroders or Henderson Global Investors sell side or buy side?

Question

They are both investment management companies, yet they manufacture investment products for institutional and retail clients??

Answer 1

"Buy side"

Sell-side are brokerages.
Buy-side are mutual funds, insurance companies, hedge funds and other asset managers.

You can even have companies that have both buy and sell-side in the same company (e.g. UBS, Credit Suisse, Morgan Stanley, Goldman Sachs). They treat each other like arms length companies in order to get the best recommendations and execution.