Sorry to hear of such unfortunate circumstances that had befallen on both of them.
Different Buddhist Traditions have different ways of expressing aspirations for the dearly departed and since you have not indicated which Tradition you belong to, it can be done as simply as making wholesome aspirations and any charitable deeds in their memory and dedicated as transference of merits (which have myriad formats/versions in different Traditions and even within the Tradition) for their well being and good rebirth like the one below taught to me many years ago:
'By the merit and virtue of this (scripture/aspiration recitation/charitable act/etc...)
May they be well and happy
May they be free from suffering and enmity
May obtain the precious human form again
May they encounter the Buddha Dharma and attain Liberation'
In my tradition, the Chinese Mahayana Tradition, it has a wide spectrum of elaborate and simple services to be done for the dearly departed and traditionally for 49 or up until 100 days from reciting scriptures, the Buddha's Name (e.g Namo Amitabha Buddha) and various Mantras all the way to charitable deeds done in their memory and its merits transferred for them.
Below are some commonly recited scriptures used:1 2 3 4 5
Since you mentioned the Four Noble Truths, this
can be recited for them as well. If you want to know the Theravada way of commemorating the dearly departed, you can post on Dharma Wheel's sister site: http://dhammawheel.com/index.php
and I am sure over there, they are more than willing to assist you.
Hopefully, my other learned brethren here on this site can also share with you from their various and respective Traditions on the how to's.