Lao vs. Laotian in English
Use of Lao
'LAO' = ຄົນລາວລຸ່ມ ແລະ ພົງສະທອນຄົນລາວລຸ່ມ
In the Lao language (and as well as in Isan—which Isan people also call LAO—and the Thai language), 'LAO' (ລາວ) can mean someone that is from the Lao People's Democratic Republic of Laos, as well as specifically ethnic Lao people (which excludes the Hmong, Khmu and others) or all people of Laos (which includes the Hmong, Khmu and others).  Isan people use 'LAO' to also refer to themselves and their language since most Isan people descend from Lao people from Vientiane, Champassak, Louang Phrabang, and other areas that are now in the Lao People's Democratic Republic.  Since this article is in ENGLISH (ພາສາອັງກິດ), English-language conventions should be used.  'LAO' in English ONLY refers to the ethnic Lao people and DOES NOT INCLUDE the Hmong, Khmu and other minorities that live in the Lao People's Democratic Republic.
Use of Laotian
'LAOTIAN' = ຄົນທີ່ມາຈາກສາທາລະນະລັດປະຊາທິປະໄຕປະຊາຊົນລາວ)
'LAOTIAN' means anything that has to do with the country of Laos as a whole.  'LAOTIAN' as a term in English INCLUDES the Hmong, Khmu, and other people that currently live in Laos and have Laotian citizenship.  If someone want to specifically refer to people (of any ethnic background) of Laos, 'LAOTIAN' should be used.

Lao including/excluding Isan
There seems to be no consensus on whether or not Isan are Lao people.  But other articles on Wikipedia seem to not differentiate this nationality vs. ethnicity debate.  

There are Swiss-Italian people, i.e., people who are ethnically Italian but live in Switzerland (not Italy).  The article about the Italian people includes Italian-Americans, Swiss-Italians, and many other people of Italian descent besides those in Italy. Obviously those in Switzerland do not have any allegiance to the Italian Government, but it does not diminish their Italianess.  The ethnic Germans can be found across Europe, and many outside of Germany, but these people are ethnic Germans, identify as such, and most likely, have no allegiance to Germany.  

The easiest solution, given how the English language works:  Make one page Laotian People (anyone from Laos, excluding Isan people and others) and make one page for Lao People, which includes Isan people.  Political allegiance to the Thai king does not mean that Isan people stopped eating sticky rice, listening to morlam, believe in Phaya Nak, celebrate Boun Phra Vet, think the Mekong River is sacred, or refer to themselves as Lao.  And Isan people have not stopped speaking the Lao language, it just got a name change.  The Isan language article has been vandalised, so to speak, with someone changing 'Isan' to 'Isan Lao'—most likely by a Lao person—since this nomenclature is absent in the speech of Isan people, who refer to themselves as 'Lao' or 'Isan' or 'Thai Isan'.  There is confusion between Thai and Lao culture, because it is almost the SAME!  Just like it's hard to tell Canadians and Americans apart, because, with the exclusion of the Québecois, people in Canada and America have the same culture, language, and share a border.  Laos and Thailand are no different.  The only thing that prevented Laos from being part of Thailand is the French, and the French are also the only ones that made the Isan people Thai, i.e., part of the Thai nation, but even the French were unable to stop Lao and Isan people from being a common people.  Isan was part of Lanxang just like Laos is, so both groups can claim access to the same heritage, influences, and what not.  Lao people make up only 50% of the population, in Isan, Lao speakers make up 88% of the region, so it is more homogenously 'Lao' than all of Laos!  Blame the French for the uneven distribution of the Lao people, but yes.  The Central Thai, i.e., Bangkok people and People of the Chao Phraya River valley, have worked very hard to integrate Isan into Thailand and claim Isan culture (which is Lao) as part of its cultural milieu.  There are also Lao that claim that the Thais have stolen from Lao culture, but since Thai and Lao (and Isan) are all descended from the same Tai peoples, of course there are similarities.  There were even Isan communists supporting integration of Isan into Laos up until the 1980s.  If the Isan people are not going to be listed as 'Lao People' than the following 'Lao' people should be removed because they are Isan by birth:
 ຫຼວງປູ່ມັ່ນ ພູຣິທັຕໂຕ Mun Bhuridatta, born in Ubon Ratchathani Province (I'm pretty sure this is Isan).
 ໜູຮັກ ພູມສະຫວັນ Nouhak Phoumsavanh, born in Mukdahan Province (again Isan).
 ມະຫາສິລາວົງ Mahasilavong, born in Roi Et Province (Isan, not even on the Mekong River)