Kailangan pa bang ipagpaalam sa MIL ko na sinama kami ng asawa ko sa company outing nila sa puerto? Lo is 6mos old

No need of course. Unless you live in her house, so as a sign of courtesy and respect you should at least inform her that you'll be out of town for a while.

Hindi naman siguro ipagpaalam pero at least alam nya (and your own parents) kung san kayo para kung may emergency, they know your whereabouts