S'entre-soutenir is a french third group verb. So, this verb is irregular and do not follow a regular conjugation pattern like first or second group verbs. Follow this link to see all the endings of the conjugation of most of the third group verbs : 
conjugation rules and endings for the second group verbs.
																												
																																					Verbs derived from 
tenir and 
venir form a major group of verbs who gains a 
d in the future and conditional. These verbs are the only verb to have a nasal vowel in the past historic and imperfect subjunctive.																												
																																																																		
The verb 
s'entre-soutenir is a reflexive verb which is always reflexive. So it is always conjugated with a reflexive pronoun. Here is the list of the french reflexive pronouns: 
« me », 
« te », 
« se », 
« nous », 
« vous », 
« se ».
																																																	
S'entre-soutenir is conjugated in interro-negative form. The interro-negative form being obtained by inversion of the subject, the placement of the negative adverb follow the same rules as in negative form, giving the following rules:
									
 - in interro-negative form, the adverb 
« ne » is always placed first if the subject is a pronoun.
									
 - in simple tenses, the adverbs (
« ne ...pas », 
« ne...plus », 
« ne...jamais », etc...) surround the verb 
s'entre-soutenir and the inverted subject pronoun.
									
 - in compound tenses or in passive voice, the negative adverbs surround the auxiliary and the inverted subject pronoun.
																			
 - With a reflexive verb, in simple tenses, the negative adverbs surround the reflexive pronoun, the verb, and the inverted subject pronoun.
										
 - With a reflexive verb, in compound tenses, the negative adverbs surround the reflexive pronoun, the auxiliary, and the inverted subject pronoun.
																		
																			
For sound reasons, like in interrogative form, an euphonious 
« t » is added to the pronoun of the third person: 
« il », 
« elle », 
« on », 
« ils », 
« elles » except when the verb ends with 
« t » or 
« d »: 
« ne s'entre-soutiendra-t-elle pas ? », 
« ne se sera-t-elle pas entre-soutenue ? ».
																											
Finally, the interrogative form does not exist in subjunctive and imperative.