Sorting categories into list put single one at end of it
Is there a reason why you don’t just drag the “Others” category to the end in the CP? The sort order will be the same for the front-end with your code:

{% set entryIds = craft.entries.section('toys').ids() %}
{% set categories = craft.categories({
    relatedTo: { sourceElement: entryIds },
    group: 'brands',
}) %}


I corrected your code, you never append another .craft.categories criteria model to a criteria model. Have a look at the docs for the allowed syntax: 

https://craftcms.com/docs/templating/elementcriteriamodel

Update:

Here’s example code that should work to list the categories alphabetically with the special “Others” category listed at the end.

{% set entryIds = craft.entries.section('toys').ids() %}

{% set categories = craft.categories({
    relatedTo: { sourceElement: entryIds },
    group: 'brands',
    order: 'title',
}) %}

{% set otherCategory = null %}

{% for category in categories %}
    {% if category.id == 72 %}
        {% set otherCategory = category %}
    {% else %}
        &lt;a href="{{ category.url }}"&gt;{{ category.title }}&lt;/a&gt;
    {% endif %}
{% endfor %}

{% if otherCategory %}
    &lt;a href="{{ otherCategory.url }}"&gt;{{ otherCategory.title }}&lt;/a&gt;
{% endif %}