The main English-language reference consulted for this branch names no aggregate speaker-population estimate for the Khasi-Palaungic branch as a whole.
What would resolve this A specialist source (Sidwell 2011/2018 or a dedicated Austroasiatic comparative study) giving an aggregate speaker count across the branch's Khasic and Palaungic groups.
OpensociolinguisticsWikipedia: Khasi-Palaungic Languages