[Several link targets for one banner?]

No, that's not possible.

To accomplish that you have to create multiple copies of the banner. 

[Add html5 banner in Revive 4.1.1 gives PHP fatal error: Cannot redeclare Plugin_BannerTypeHTML_delivery_adRender]

When I add a html5 banner to a campaign in Revive 4.1.1 and click 'save changes', I get an empty page in the admin. The Apache error log contains:

PHP Fatal error: Cannot redeclare Plugin_BannerTypeHTML_delivery_adRender() (previously declared in /home/applinet/local/ads/www/lib/OX/Extension/bannerTypeHtml/bannerTypeHtmlDelivery.php:31) in /home/applinet/local/ads/www/lib/OX/Extension/bannerTypeHtml/bannerTypeHtmlDelivery.php on line 31

What may be causing this?

I'm using Revive 4.1.1 (upgraded from 4.0 and OpenX before that) with PHP 7.0 and MySQL 5.5 on Debian 9.2 Linux.