No, you can't. In the various masculine, feminine, singular and plural:
-celui-ci/là est petit
-celle-ci/là est petite
-ceux-ci/là sont petits
-celles-ci/là sont petites
You can use celui, celle... in another type of construction:
-je veux celui / celle qui a des boutons noirs
-je veux ceux / celles qui ont des boutons noirs
Ce means this or that. Ceci is a combo of [ce + ici] (this here) and cela a combo of [ce + là] (that there).
I forgot to answer your other question. There is not much difference in meaning with ce sont petits except it does not specify if you mean these or those. Also celles/ceux really mean these ones or those ones. I am not sure but I believe you can uses cela in place of ce in ce sont petits to mean those are small.
ETA: Ignore that last statement. See Sitesurf's comment below. I should have known better because I know cela means "that" so is singular.
Celle(s), celui, and ceux cannot stand alone. They have to:
have the suffix -ci or -là, which specifies if you mean something close by or farther from you;
be followed by a relative pronoun (que, qui, etc.) and a dependent clause:
"The apples are the ones that your mother bought" - Les pommes sont celles que votre mère a achetées
- be followed by de:
le robot est celui de l'enfant (the robot is the child's)
Celles means "these ones" or "those ones". Celles-là means "those ones", indeed, but in English, you can drop "ones" and just say "those" and it still means the same thing.
This has been explained a few times in the discussion--a fact you would have known if instead of rushing to post whenever you have a question, you read the discussion first. Please make it a habit to read first to avoid redundant questions.
Duo, whose English is American-based, thinks "ones" in "those ones" is redundant and that it should only be "those". I personally don't have a problem with your usage.
Here is what Grammar Girl says: https://www.quickanddirtytips.com/education/grammar/these-one
Here is another article on this: https://www.dailywritingtips.com/these-ones-vs-those-ones/
And here is an interesting argument for it: https://www.grammarphobia.com/blog/2014/08/these-ones.html
Because that is not proper grammar. It falls in the same category as "all y'all". The word "those" already includes the nuance that the items are there not here. So it is redundant and wrong to add "there".
"Those are small" is the proper way to talk about things that are over there.