In the notifications you can use placeholders (e.g. %%USER_LASTNAME%%) to output some of the standard user fields, but looking at your form you are not using the standard fields for first name, last name, email etc.
Here are the defaults in a new registration form for those fields:
<div class="form-group">
<label>[cred_i18n name='user_email-label']Email[/cred_i18n]</label>
[cred_field field='user_email' class='form-control' output='bootstrap']
</div>
<div class="form-group">
<label>[cred_i18n name='first_name-label']First name[/cred_i18n]</label>
[cred_field field='first_name' class='form-control' output='bootstrap']
</div>
<div class="form-group">
<label>[cred_i18n name='last_name-label']Last name[/cred_i18n]</label>
[cred_field field='last_name' class='form-control' output='bootstrap']
</div>
Note that the field slugs are "user_email", "first_name", and "last_name".
In your form the field slugs are "email", "peer_first_name", and "peer_last_name".
So you are using custom user fields, not the standard fields, hence those placeholders such as %%USER_LASTNAME%% can't be used to output your custom user field values.
And actually, you are doing it wrong anyway, because to output the standard Last Name you would simply use %%USER_LASTNAME%% directly, and in your case you are trying to use them as user_id attributes in your shortcodes.
In this example here you are not even outputting your custom user fields, you are trying to output the standard fields via shorcode, but the shortcodes are broken because you pass the placeholders as user_id attributes:
First Name: [wpv-user field="user_firstname" user_id="%%USER_FIRSTNAME%%"]
Last Name: [wpv-user field="user_lastname" user_id="%%USER_LASTNAME%%"]
Email Address: [wpv-user field="user_email" user_id="%%USER_EMAIL%%"]
If you want to output the standard fields for last name etc. then just use the placeholders directly, e.g.
Last Name: %%USER_LASTNAME%%
If you want to output your custom user fields, then use the shortcodes but include the user_id attribute like so:
Last Name: [types usermeta='peer-last-name' user_id='%%USER_USERID%%'][/types]
(That types shortcode to output a user custom field can be inserted using the Fields and View button in the notification editor, but you need to add the user_id attribute manually.)
I think the first thing you need to do is decide whether you are using the standard WordPress fields for first name, last name, and email and whether you need custom fields for those at all, and once you decide that you can use the above to determine how to use those fields in the notifications.
Hopefully that helps. I realise it is not the easiest of things to implement, and it is on our to-do list to improve the usability of these features.
