Is offering regular prayers valid in a graveyard that was originally designated as a Janazgah (burial ground)?

Aslaam O Alaikum, Iam a retired Bio Statistician from Health department Punjab and from a lonely local muslim family. Out of four ,there is only one muslim graveyard left for burials of bodies whereas 6 Mosques are functioning for offering prayers.In order to grab the land of this graveyard an outsider unqualified person with the help of few other outsiders first changed Janazghah of graveyard to a Mosque and installed himself as Imam alongwith loud speakers to offer faraz namaz in place of offering Namaz e Janaza in this graveyard on the pretext stated above.He with the connivance of other illiterate persons ,have stopped muslims to offer Namaz e Janaza in the Origional Janazgah (constructed about 150 years ago). He also indulge in taveej Ganda and misquiding villagers with the un Islamic acts of this ugly business. When he is asked to stop compelling people to offer Namaz e janaza outside under trees instead of Mosque, he argue that dead bodies is not allowed to place inside for Namaz e Janaza as this is now being used for faraz Namaz and thus harassing muslims .So far as his reputation is concerned a case of sexual abuse is also in the court against him and his group members.Will you please kind enough to guide us in the light of shariat and Hadees whether faraz namaz is valid in grave yard and whether his act of stopping Namaz e Janaza in the mosque(Janaz gah) existing in the graveyard for 150 years is valid or invalid . How can this problem created by few out siders can be solved and this graveyard can be protected for future use . Here in Punjab many graveyards have been converted into colonies with the connivance of Wakf Board employees as our population is meagre and their illegal acts go un checked. Kindly guide us to enable us to protect graveyards from aforesaid elements.Here it again pointed out that six mosques are being used in the city for prayers with Imams appointed by Wakf Board whereas four graveyards have totally vanished. Expecting early reply.Whether namaz-e-janaza and farz namaz simultaneously valid in this mosque of greyard originaly busilt as janazgah for offering namaz e janaza Allah Hafiz Mohammad Afzal