How should I handle reviewer comments when grammar makes the meaning unclear?
First, work through the comments with someone else to parse their meaning as closely as possible. A native speaker might be able to explain what the reviewer was trying to say in his/her comments. If several people are not able to understand or do not agree, then you may contact the editor for clarification. But try not to reach this point--nothing in the snippet you have provided seems that problematic.

Next, revise and resubmit as directed by the journal editor. In your response to reviewer comments, I would create a numbered list of comments. Before stating how you addressed each comment, you should briefly restate your understanding of what the comment was conveying. If you have not adequately addressed the comment because you did not understand it, then this should at least prompt the reviewer to clarify their comment, rather than become annoyed at your response.