Both of the deals are subject to recall clauses.
Attacking midfielder Williams was on target for the Tigers in their 3-1 home win over Leamington last Saturday, with ex-Robins man Adam Connolly also on target at Whaddon Road.
Academy products Bowen and Williams have both signed contracts with Cheltenham until the end of next season. Bowen has made one start and one substitute for the Robins' first team, while Charlton Kings-based Williams has made five starts and seven substitute appearances.
Striker Bobbie Dale is on loan at Cinderford Town for the rest of the campaign and he too has another year left to run on his contract.