@ wineisallforme,
Indeed, you have a bit of a complex problem. How you proceed will involve some research and clear understanding of the laws.Â
First, I suggest you/your family do the following;
1. Take note of how the land is currently titled and in who's name it is in. If in your mom's name it must be a TCT (Transfer Certificate of Title), if in past relatives name(s), it could be TCT or OCT (Original Certificate of Title). This is a must do to learn/understand as the next steps unfold.Â
2. Get very familiar with RA7279 and decide how you want to proceed.
3. By understanding the term "Professional Squatter" you should proceed to the Brgy with a clearly worded "immediately cease and desist from squatting" letter that is placed in the Brgy blotter for each squatter family/group/person.
Here is an example of what I have prepared a few months ago for a friend in this same situation:
"To:Â Â Â ____________________, Brgy. Captain
Brgy. ________________
Davao Del Norte, Republic of the Philippines
cc: Mayor __________________
Monday, April 20, 2020
Subj:  Demand for “Professional squatter†(i.e., ________________ at el) to immediately cease from squatting and vacate my land.
Dear Brgy ______________________,
Void of any Affidavit of Consent from me (the land/lot owner) for the construction of any building/house, please find attached herein my demand for “Professional squatter†(i.e.,___________, at el) to immediately cease and desist from squatting, and remedy by complete removal of any/all unauthorized structures and or modifications to my land and vacate my land as provided under RA 7279.Â
The below listed demands are herein detailed as follows:
1.  The squatter ________________, at el, has 30 consecutive calendar days to cease all habitat functions.
2.  The squatter _______________, at el, has 30 consecutive calendar days to cease any/all agriculture operations including but not limited to; planting, harvesting, cultivating and or irrigation activities.Â
3.  The squatter ______________, at el, has 30 consecutive calendar days to remove all structures, houses and or buildings from my land.Â
4.  The squatter _______________, at el, has 30 consecutive calendar days to restore my land back to the conditions which he found the land; free of debris, trash or structural remains.
5.  The squatter _____________ at el, has 30 consecutive calendar days to properly clear and remedy any sewage, septic tank, or residential waste processing or related unauthorized structures from my land.
Captain __________, please officially receive and blotter this demand letter, than formally serve squatter ___________ at el, immediately."
Please note that this will need to be done with each family/group you know to be on your land in an unauthorized manner.
4. The farmers living with permission on the land is a very different set of actions and should be done with as much past documentation to ensure all rights are protected.Â
In general, all of the above will cause a hard look at property lines and could result in the need to sub-divide in order for the farmers to be able to purchase their "selected" lot, if offered & accepted.
In all your demands to the Brgy (and later to any court), you want to consider ending your correspondence with, " My intentions are to summarily evict the “Professional squatter(s)†on my land known as “________________†under the provisions of RA 7279."
Also, be clear about how this situation is and continues to impact your family. Part of the document I prepared stated the following:
This “Professional Squatter†has and continues to harm me and my family as follows:Â
1.  There are no plans to place any structures on my land, nor are there any boundaries stated/clarified to be for residential use,
2.  There are no plans to update my land tax status to include declaring any and all structures placed on my property by “____________â€,
3.  My land is farm land and has not been approved for any sewage or residential waste processing,
4.  This land has great emotional significance to me and my children since it represents land intentionally left under-developed, per my, and my ancestor’s wishes,
5.  The act of building a structure and living on my land results in both ground/soil and water pollution.
In Summary,
It is not my intent to claim this is ALL that needs to be done or that the process can be accomplished in a few letters. However, do not make the mistake of failing to start at the Brgy level and ending with a case dismissal at the trial court (RTC). You do not need an atty to start the process, as outlined above. However, you/your mom will need to start at the Brgy to make any case stick.
The very best to you/your family in solving this matter.