Sec. 11, Art. VI (Legislative Dept.), of the 1987 Constitution provides that "a Senator or Member of the House of Representatives shall, in all offenses punishable by not more than six years imprisonment, be privileged from arrest while the Congress is in session". (It also provides that "no member shall be questioned nor be held liable in any other place for any speech or debate in the Congress or in any committee thereof."). Pro-Duterte Speaker Alvarez should be aware of this basic constitutional provision (to moderate his harassment of Sen. De Lima).
Although in "indirect contempt" cases, a judicial tribunal or Congress may detain a witness until such time that he performs an act that was ordered to be done, such power presupposes that the order does not violate the constitutional right of the witness against "privacy" and "self-incrimination" (the right to be left alone and the right to remain silent). The witness may invoke such rights at the proper time.
As far as I know, the rules of procedure of the Lower House do contain any provision expressly empowering it to arrest a member of the Upper House. What is clear, though, is that both Houses must observe the traditional common-law doctrine of "inter-parliamentary courtesy".
It will be noted that under Sec. 7, Rule 71 (Contempt) of the Rules of Court, indirect contempt is punished only by imprisonment of not more than six months and/or a fine of thirty thousand pesos only.
As to the crime of "obstruction of justice", Senate President Pimentel has told reporters the other day that the penalty for such an offense is only four years.
My personal position is that the Senate must preserve its collegial dignity as a constitutional body. It must not allow itself to be bullied by the Lower House, which is notorious for being a den of Duterte fanatics, trapos, and feudal lords like him. The Senate must reject outright any written order from the Lower House commanding the "arrest" of De Lima for "indirect contempt". (In the first place, the Lower House should have never subpoenaed De Lima as a witness in its committee hearings from the very start, the same being violative of the timeless doctrine of "inter-parliamentary courtesy".