If both Third Orders and seculars can be either a priest/cleric or a layperson, then I’m still not quite sure what the difference is…?
As with all simple explanations (especially about the Franciscan Order) this is over simplified but in general this is the makeup.
1st Order - Primarily consists of OFM, OFM Conventual and OFM Capuchin. There are also a few groups of groups that have direct heritage from those groups, but not a lot. All members of this order are Religious. Some are ordained, some aren’t all depends on the needs of the Order.
2nd Order - These are the only people that could be considered nuns. Most are cloistered. Almost ALL actual 2nd Order sisters have Clare somewhere in their name. Usually Poor Clare. Most other Franciscan female groups are usually 3rd Order. All are religious, none are ordained.
3rd Order Religious - Largest group is TOR. MOST Franciscan sisters that you actually meet fall under this category. MOST Franciscan friars that aren’t part of the 1st Order also fall in this category. All are religious, some are ordained, some aren’t all depends on the needs of the group.
3rd Order Secular - Officially the only group that falls in this category is the Secular Franciscan Order (OFS). There are a few groups that call themselves something different, but still use the Secular Franciscan Order rule and usually support particular missions, but are still under the umbrella of the OFS. There are no religious brothers or sisters, but there are secular priests and deacons as members. Most of the secular priests are usually diocesan priests that may have felt a calling to follow Franciscan ideals after they were ordained. The secular deacons are mixed, some had their calling to OFS before joining, others after. Members make promises not vows, some make private vows but they aren’t required.
One major thing to remember based on your original question is that being a priest within the Franciscan Order doesn’t make you any better then a person that isn’t ordained. Under the ideal within the Order, each group only ordains as many priest as are absolutely for their mission. At the friary I go to you will see the priests mopping the floor, washing dishes, etc. Sometimes the person in charge of friaries are not ordained. There is definitely no guarantee that if you enter a Franciscan group wanting to eventually be a priest, that you will become one. There have been abuses in the past where Franciscan priests felt that the non-ordained were there as servants, but most of the Order is seeking to return to the ideals of the founders.
Of course this post only covers the official Orders, there are numerous Franciscan associations, lay groups, etc. that aren’t officially covered under “orders”.