AsalamoAlikum
Is it an absolute obligation on a believer to ask others to come with him to the mosque if he is leaving them for it. Kindly take into accounting following situations:
A person sitting in a gathering and knows that people get offended if he tells them to come to the mosque. These people usually do not like dication from others. If you invite them then next time they would want to avoid you somehow. It seems more appropriate to work on their Iman whilst in between them and let them decide for themselves whether to goto mosque or not. Is it ok to treat them with kindness and somehow indirectly work on them and let them take heed. Finally leave for the mosque and do not directly tell them to come with you since currently they do not tolerate that.
Some People are so busy in their schedules these days. They try to avoid people who they believe will ask them to come to mosque if they meet randomly. If you meet them and do a nice dawah through your behaviour and attitude(e.g. deal with them with nice Ikhlaq) then it makes an impact but they do not like at that moment to receive invitaion to Mosque. Is it ok to just do a nice dawah through behaviour whilst meeting these people and not inviting them for the mosque. In other words, let them not avoid you since they know that you will not ask them to come to mosque. Work on them using nice Ikhlaq and let them take heed.
Jazak Allah

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

First of all, you should know that enjoining good and forbidding evil is one of the most important rites of Islam and one of its most important pillars. Moreover, this is an obligation according to one’s ability but the scholars clarified that the benefits and harms should be taken into account in enjoining good and forbidding evil. Therefore, if forbidding evil leads to another greater evil, then it is not permissible to forbid it in this case, if the evil is removed but it is replaced by another similar evil, then one should study the case (to choose between the two), and if the evil is removed and is not replaced by another evil, or that it is replaced by an evil smaller than it, then it is an obligation to forbid it in this case.

The majority of the scholars say that knowing or predominantly thinking that the person who is enjoined will not benefit from that is not a sound reason for not enjoining good and forbidding evil because establishing the evidence against a Mukallaf (a man/woman who is competent for religious assignments) and the manifestation of the rites of Islam is one of the objectives of enjoining good and forbidding evil. Forbidding evil should be as Allaah Says (what means): {“To be absolved before your Lord and perhaps they may fear Him.”}[Quran 7:164] Indeed, this balance is very delicate and subtle and it requires keeping one’s desires aside. That is because one’s desires may suggest to him/her that not enjoining good is the benefit whereas it is not the case.

Based on the aforementioned points, you should enjoin good and forbid evil whenever this is possible while being keen on doing so in a wise manner and good admonition and seeking the best means that does not lead the addressee to feel averse to you. Fearing that your status with them may be undermined or them keeping away from you should not prevent you from doing so.

If you know or predominantly think that he will not be benefited if he is admonished now, and he may be repelled in a way that it will be impossible for him to be benefited from your admonition, and you rather know or predominantly think that if you deal step by step with him and advise him gradually, this will affect him and leads him to take heed, then this is permissible to do so as the objective is that he should be benefited.

However, if you know or predominantly think that he totally rejects advice and that being kind to him is of no use, then you should take the initiative to advise him in order to be acquitted from sin and establish evidence against him.

Besides, you should know that the prayer is of great importance and a person who abandons it is in a very dangerous situation. Therefore, you should remind your brothers (in Islam) of this meaning and clarify to them that a person who abandons the prayer is worse than the person who commits Zina (fornication or adultery), steals, consumes intoxicants, or murders according to the consensus of the scholars and that such a person is exposing himself to the immediate and delayed Punishment of Allaah. Moreover, some scholars are of the view that a person who abandons the prayer becomes out of the fold of Islam; for more benefit, please refer to Fatwa 85264.

As regards the congregational prayer, there is a difference of opinion among the scholars as to whether or not it is an obligation, and the most preponderant opinion is that it is an obligation on pubescent men; for more benefit, please refer to Fatwa 82538.

Besides, the scholars who are of the view that the congregational prayer is an obligation, believe that it is not an obligation to perform it in the mosque; rather, if it is performed at any other place than the mosque, it would be sufficient, and the obligation would be waved off even though the excellence of performing it in the mosque is missed. Hence, dear brother, you should not refrain from advising the people who abandon the prayer as we have made it clear to you that the prayer is so very important in Islam.  

Allaah Knows best.