Sample Code:

Aura Component:

<aura:component implements="force:appHostable" >  
      
    <aura:attribute name="selectedVal1" type="String" default="Not Sure" />  
    <aura:attribute name="selectedVal2" type="String" default="No" />  
    <aura:attribute name="options"   
                    type="List"   
                    default="[{'label': 'Yes', 'value': 'Yes'},  
                              {'label': 'No', 'value': 'No'},  
                              {'label': 'Not Sure', 'value': 'Not Sure'}]"/>    
      
    <div class="slds-box slds-theme_default">  
          
        <lightning:radioGroup label="Select Option"  
                              options="{! v.options }"  
                              value="{! v.selectedVal1 }"  
                              type="button"  
                              variant="label-inline"/><br/><br/>  
          
        <lightning:radioGroup label="Select Option"  
                              options="{! v.options }"  
                              value="{! v.selectedVal2 }"  
                              type="radio"  
                              variant="label-inline"  
                              style="display:inline-block !important"/>  
          
    </div>  
      
</aura:component> 

Aura Component Style:

.THIS .slds-radio {  
    display: inline !important;  
} 

Output: