When they arrive in the first and last sliders they put the slides all as .active

      $(document).ready(function(e) {
                    
        const blocos = $("div.slider div.slide div");
        
        function startslider() {  
        
          ativa = $(".ativa")
          
          if (!$(ativa).next().length) {
              ativa = blocos.first()
          }
          
           $(ativa)
              .removeClass("ativa")
              .next()
              .addClass("ativa")
          
           setTimeout(startslider, 5000)
        }
        
        setTimeout(startslider, 5000)
        
        $("div.slider nav button.anterior").click(function(){
        
          prev = $(".ativa").prev();  
          prev = prev.length ? prev : blocos[ blocos.length - 1 ];  
          mostraBloco(prev);
          
        })
        
        $("div.slider nav button.proximo").click(function(){
            
          next = $(".ativa").next();    
          next = next.length ? next : blocos.first();    
          mostraBloco(next);
          
        })
        
        /* Função para exibir as imagens */
        function mostraBloco(next) {
            
          ativa = $(".ativa")          
          $(ativa).removeClass("ativa")
          $(next).addClass("ativa")
          
        }
      });

      * {
          margin: 0;
          padding: 0;
          border: none;
          outline: 0;
      }
      body {
          width: 100vw;
      }
      ul {
          list-style: none;
      }
      .fade {
          -webkit-animation-name: fade;
          -webkit-animation-duration: 1.5s;
          animation-name: fade;
          animation-duration: 1.5s;
      }
       @-webkit-keyframes fade {
       from {
       opacity: .4
      }
       to {
       opacity: 1
      }
      }
       @keyframes fade {
       from {
       opacity: .4
      }
       to {
       opacity: 1
      }
      }
      @keyframes slider {
       0% {
       transform: scale(1);
      }
       100% {
       transform: scale(1.1);
      }
      }
      div.slider {
          position: relative;
          width: 100%;
          overflow: hidden;
      }
      div.slider div.slide {
      }
      div.slider div.slide div {
          display: none;
      }
      .ativa {
          display: block !important;
          animation: fade 1s linear;
      }
      div.slider div.slide div img {
          position: relative;
          width: 100%;
          animation: slider 1s linear;
          animation-fill-mode: forwards;
      }
      div.slider div.slide div span {
          position: absolute;
          width: 100px;
          left: calc(50% - 50px);
          line-height: 40px;
          bottom: 0;
          text-align: center;
          color: rgb(255,255,255);
          z-index: 2;
      }
      div.slider nav {
          position: absolute;
          width: 100%;
          height: 40px;
          bottom: 0;
          background-color: rgba(0,0,0,.5);
          z-index: 1;
      }
      div.slider nav button {
          position: absolute;
          width: 150px;
          height: 100%;
          cursor: pointer;
      }
      div.slider nav button.anterior {
          left: 10%;
      }
      div.slider nav button.proximo {
          right: 10%;
      }

	<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><divclass="slider">
    
      <div class="slide">
      
       <div class="ativa">
         <img src="http://funerariasaopedro.net.br/novo/_img/_banner/_site/bg_1.jpg"/><span>Esteé1</span></div><div><imgsrc="http://funerariasaopedro.net.br/novo/_img/_banner/_site/bg_2.jpg" />
         <span>Este é 2</span>
       </div>   
       
       <div>
         <img src="http://funerariasaopedro.net.br/novo/_img/_banner/_site/bg_3.jpg"/><span>Esteé3</span></div></div><nav><buttonclass="anterior">Anterior</button>
      <button class="proximo">Próximo</button>
     </nav>
    
    </div>