As the others said, as long as the trades are kept fair to both sides there won't be any problems. Its an issue if one account is regularly benefiting from the other. I did also want to add that there is more info in the side rules
here, specifically the section that starts with "Each user may have one account" details a more specifics.
A few things that are good to remember;
- If you ever want to do a large trade or gift with each other and are worried it might be flagged, you can send in a
help ticket to ask if the trade would be ok to make before you complete it. That way you can get confirmation that it won't flag your accounts.
- CS doesn't allow off-site trades for things that aren't other pet sites (such as trading CS for Flight Rising would be fine, but not for Fortnite stuff). I mention it cause sometimes siblings/friends will offer each other pets for doing favors irl. Thats not considered a legitimate trade. Again would suggest making use of help tickets to check with CS staff first if you aren't sure if a specific trade/gift would be ok to not.
- If one of you decides to quit/leave CS, don't send everything to the other person. It'll almost certainly end up being flagged as cheating, its recommended that beyond the regular parting gifts, the pets be sent to the pound instead, or given away on the free adoptions board. Staff can also help with mass transfers of pets in these cases (such as sending everything to the pound for you).
Also wanted to add that its always fine to send in a help ticket with general questions for staff, especially for this sort of thing or if you want to ask about a specific scenario that only staff would be able to help with ^^